Vehicular drive system

ABSTRACT

A vehicular drive system accommodated in a housing and including a first input shaft that receives a vehicle drive force generated by a vehicle drive power source, and a differential mechanism operable to distribute the vehicle drive force received from the first input shaft to a first electric motor and a second input shaft. The first and second input shafts are disposed coaxially with a first axis such that the second input shaft is disposed downstream of the first input shaft. The first input shaft is rotatably supported by a first support portion provided on the housing and an axial end portion of the second input shaft, and the second input shaft is rotatably supported by a third support portion and a fourth support portion that are provided on the housing.

TECHNICAL FIELD

The present invention relates to a vehicular drive system including afirst electric motor, a differential portion, a second electric motorand a transmission portion, and more particularly to techniques forreducing the axial dimension of the vehicular drive system and improvingaccuracy of assembling of the vehicular drive system.

BACKGROUND ART

There is known a vehicular drive system including a first electricmotor, a differential portion, a second electric motor, and atransmission portion. JP-2003-301731A discloses an example of such adrive system for use on a hybrid vehicle. In the hybrid vehicle drivesystem disclosed in this publication, the first electric motor,differential portion, second electric motor and transmission portion aredisposed coaxially with each other, such that they are arranged in theaxial direction of the drive system in the order of description.Accordingly, the required axial dimension and width dimension of thisvehicular drive system tend to be large. In particular, where thevehicular drive system is transversely installed on an FF (front-enginefront-drive) vehicle or an RR (rear-engine rear drive) vehicle, thistransverse installation of the drive system is difficult due to alimited space available for installation of the drive system on the FFor RR vehicle. For example, the drive system including the transmissionportion as described above is installed on a hybrid vehicle known as“PRIUS” (registered trademark), an extensive analysis is requiredregarding the layout of the components of the drive system, so that thedrive system can be installed within the limited width dimension of thehybrid vehicle. It is also noted that among an increased number ofcomponents of the drive system, the electric motors and the transmissionportion that are assembled together have a relatively large number ofrestrictions in the assembling, the overall efficiency of assembling ofthe drive system tends to be considerably lowered. Thus, there has beena need for providing a vehicular drive system which has a reduced axialdimension and an improved accuracy of assembling.

It is considered to provide a vehicular drive system which has aplurality of parallel axes and in which the first electric motor,differential portion, second electric motor and transmission portion arearranged in a plurality of power transmitting paths on the respectiveparallel axes. However, no techniques have been available for adequatelylaying out the components of this type of vehicular drive system, whichcomponents include a housing structure consisting of separate housingportions. An inadequate layout of the components on the plurality ofparallel axes does not permit sufficient reduction of the axialdimension of the drive system, and has a risk of deterioration ofaccuracy of support of various rotary members of the drive system.

DISCLOSURE OF THE INVENTION

The present invention was made in view of the background art describedabove. It is therefore an object of the present invention to provide avehicular drive system which has a reduced axial dimension and animproved accuracy of support of its rotary members.

The object indicated above may be achieved according to the principle ofthe present invention, which provides a vehicular drive systemaccommodated in a housing and comprising a first input shaft whichreceives a vehicle drive force generated by a vehicle drive powersource, and a differential mechanism operable to distribute the vehicledrive force received from the first input shaft to a first electricmotor and a second input shaft, the first and second input shafts beingdisposed coaxially with a first axis such that the second input shaft isdisposed downstream of the first input shaft, and wherein the firstinput shaft is rotatably supported by a first support portion providedon the housing and an axial end portion of the second input shaft, andthe second input shaft is supported by a third support portion and afourth support portion that are provided on the housing.

In the vehicular drive system of the present invention, the first inputshaft is rotatably supported by the first support portion provided onthe housing and the axial end portion of the second input shaft, and thesecond input shaft is rotatably supported by the third support portionand the fourth support portion) that are provided on the housing. Thus,only the first support portion, the axial end portion of the secondinput shaft, and the third and fourth support walls are used torotatably support the first input shaft and the second input shaft, withhigh degrees of radial bearing accuracy and concentricity, and the axialend portion of the second input shaft is used to rotatably support thefirst input shaft at its axial end portion, so that the required axialdimension of the vehicular drive system can be effectively reduced.

According to a first preferred form of this invention, the second inputshaft is provided with a support member in the form of a circular discsplined to an outer circumferential surface such that the support membersupports a rotary element of the differential mechanism. In this form ofthe invention, the differential mechanism and the second input shaft canbe easily assembled.

The vehicular drive system according to a second preferred form of theinvention further comprises a second electric motor disposed in a powertransmitting path between the second input shaft and a drive wheel of avehicle, and wherein the second input shaft supports a rotor of thesecond electric motor, so as to be rotated with the rotor, and the rotoris rotatably supported by said third and fourth support portions. Thus,the rotor of the second electric motor having a comparatively large loadis rotatably supported by the third and fourth support portions of thehousing.

According to a third preferred form of this invention, the firstelectric motor has a rotor rotatably supported by the first supportportion and a second support portion provided on the housing. In thisform of the invention, the first input shaft does not receive a load ofthe rotor of the first electric motor, whereby a structure forsupporting the first input shaft can be simplified.

The vehicular drive system according to a fourth preferred form of thisinvention further comprises a drive gear fitted on an axial end portionof the second input shaft that is opposite to the axial end portionthereof supporting the first input shaft. In this form of the invention,the drive gear having a comparatively large diameter and a comparativelylarge load is rotatably supported primarily by the fourth supportportion.

According to a fifth preferred form of the invention, the housingincludes three separate axial portions in the form of a cap-shaped firstcasing portion, a cylindrical second casing portion and a cylindricalthird casing portion, the first support portion being formed integrallywith the cap-shaped first casing portion, the third support portionbeing fixed to an axial end portion of the cylindrical third casingportion which is on the side of the vehicle drive power source, and thefourth support portion being formed integrally with an axial end portionof the cylindrical third casing portion which is remote from the vehicledrive power source. In the present drive system, the first input shaftis rotatably supported by the first support portion formed on the firstcasing portion, and the axial end portion of the second input shaft,while the second input shaft is rotatably supported by the third supportportion fixed to the axial end portion of the third casing portion 12 con the side of the vehicle drive power source, and the fourth supportportion formed at the other axial end portion of the third casingportion remote from the vehicle drive power source. Thus, the firstinput shaft and the second input shaft are supported with high degreesof radial bearing accuracy and concentricity. Further, the absence ofany support wall to support the first input shaft at its axial endportion remote from the vehicle drive power source, and the utilizationof the axial end portion of the axial end portion of the second inputshaft to support the first input shaft make it possible to reduce therequired axial dimension of the vehicular drive system.

In one advantageous arrangement of the third preferred form of thisinvention, the second support portion is formed integrally with saidcylindrical second housing portion. In the arrangement, the rotor of thefirst electric motor is rotatably supported by the second supportportion, and the second support portion preferably has an passage forsupplying a pressurized working fluid controlling a differentiallimiting device incorporated in the differential mechanism.

According to a sixth preferred form of this invention, the differentialmechanism is disposed radially outwardly of first input shaft, so thatthe required axial dimension of the vehicular drive system comprisingthe differential mechanism can be reduced.

According to a seventh preferred form of this invention, thedifferential mechanism is provided with a differential limiting deviceoperable to limit a differential function of the differential mechanism,and the differential limiting device is disposed radially outwardly ofthe first input shaft, so that the required axial dimension of thevehicular drive system comprising the differential mechanism providedwith the differential limiting device can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a drive system for a hybrid vehicle,which is constructed according to one embodiment of the presentinvention;

FIG. 2 is a table indicating shifting actions of the drive system of thehybrid vehicle of the embodiment of FIG. 1 operable in a selected one ofa continuously-variable shifting state and a step-variable shiftingstate, in relation to different combinations of operating states ofhydraulically operated frictional coupling devices to effect therespective shifting actions;

FIG. 3 is a collinear chart indicating relative rotating speeds ofrotary elements of the drive system of the hybrid vehicle of theembodiment of FIG. 1 operated in the step-variable, shifting state, indifferent gear positions of the drive system;

FIG. 4 is a view showing an example of an operating state of a powerdistributing mechanism of the drive system placed in thecontinuously-variable shifting state, the view corresponding to a partof the collinear chart of FIG. 3 which shows the power distributingmechanism;

FIG. 5 is a view showing the operating state of the power distributingmechanism placed in the step-variable shifting state by engagement of aswitching clutch C0, the view corresponding to the part of the collinearchart of FIG. 3 which shows the power distributing mechanism;

FIG. 6 is a view indicating input and output signals of an electroniccontrol device provided in the drive system of the embodiment of FIG. 1;

FIG. 7 is a functional block diagram illustrating major controlfunctions performed by the electronic control device of FIG. 6;

FIG. 8 is a view indicating a stored predetermined relationship used bythe switching control means of FIG. 7 for switching between acontinuously-variable shifting region and a step-variable shiftingregion;

FIG. 9 is a view indicating a stored predetermined relationship used bythe switching control means of FIG. 7, which is different from that ofFIG. 8;

FIG. 10 is a view showing an example of a manually operated shiftingdevice used to manually shift the vehicular drive system of FIG. 1;

FIG. 11 is a fragmentary cross sectional view of a part of the drivesystem of FIG. 1 which includes a first planetary gear set and twoelectric motors;

FIG. 12 is a fragmentary cross sectional view of another part of thedrive system of FIG. 1 which includes second, third and fourth planetarygear set and a final reduction gear device;

FIG. 13 is a transverse cross sectional view for explaining relativepositions of first, second and third axes of the vehicular drive systemof FIG. 1;

FIG. 14 is a flow chart illustrating a process of assembling thevehicular drive system of FIG. 1;

FIG. 15 is a fragmentary enlarged view in cross section showing thefirst electric motor, the first planetary gear set, and other componentsadjacent to the first electric motor and the first planetary gear set;

FIG. 16 is a fragmentary enlarged view in cross section showing adifferential drive gear, and components adjacent to the differentialdrive gear;

FIG. 17 is a fragmentary enlarged view in cross section showing thesecond electric motor, a drive gear, and components adjacent to thesecond electric motor and the drive gear;

FIG. 18 is a fragmentary enlarged view inc cross section showing thedriven gear, clutches C1 and C2 of an automatic transmission, andcomponents adjacent to the driven gear and the clutches;

FIG. 19 is a fragmentary cross sectional view showing an arrangement ofa drive linkage in a second embodiment of this invention;

FIG. 20 is a fragmentary cross sectional view showing an arrangement ofa power transmitting path between the differential drive gear and thefinal reduction gear device, in a third embodiment of this invention;

FIG. 21 is a schematic view showing an arrangement of a vehicular drivesystem constructed according to a fourth embodiment of this invention;

FIG. 22 is a table indicating gear positions of an automatictransmission of the embodiment of FIG. 21, which are established byengaging actions of respective different combinations of hydraulicallyoperated frictional coupling devices;

FIG. 23 is a schematic view showing an arrangement of a vehicular drivesystem constructed according to a fifth embodiment of this invention;

FIG. 24 is a table indicating gear positions of an automatictransmission of FIG. 23, which are established by engaging actions ofrespective different combinations of hydraulically operated frictionalcoupling devices; and

FIG. 25 is a schematic view showing an arrangement of a vehicular drivesystem constructed according to a sixth embodiment of this invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to the drawings, there will be described in detail thepreferred embodiments of the present invention.

Embodiment 1

Referring first to the schematic view of FIG. 1, there is shown a drivesystem 10 for a hybrid vehicle, which is constructed according to oneembodiment of this invention. The drive system 10 shown in FIG. 1includes: an engine 8; a transaxle housing 12 (hereinafter referred tosimply as “housing 12”), which is a stationary member attached to thebody of the vehicle; a pulsation absorbing damper (vibration dampingdevice) 9; a first input shaft in the form of an input rotary member 14connected to the engine 8 through the pulsation absorbing damper 9 andreceiving an output of the engine 8 through the pulsation absorbingmember 9; a first electric motor M1; a hydraulically operateddifferential limiting device in the form of a switching clutch C0 and aswitching brake B0; a differential gear mechanism or differentialportion in the form of a power distributing mechanism 16 connected tothe input rotary member 14; a second input shaft in the form of a powertransmitting member 18 disposed downstream of the first input shaft; asecond electric motor M2; a step-variable transmission in the form of anautomatic transmission portion 20; and an output shaft in the form of anoutput rotary member 22. The above-indicated components 9, 14, M1, C0,B0, 16, 18, M2, 20, 22 are all accommodated within the housing 12, andthe components 9, 14, M1, C0, B0, 16, 18 and M2 are disposed coaxiallywith each other on a first axis CL1, while the components 20 and 22 aredisposed coaxially with each other on a second axis CL2 parallel to thefirst axis CL1. A drive gear 19 located at one axial end of the firstaxis CL1, and a driven gear 21 located at one axial end of the secondaxis CL2 and meshing with the drive gear 19 cooperate to constitute adrive linkage 23, which is a part of a power transmitting path betweenthe engine 8 and the output rotary member 22. The automatic transmissionportion 20 is disposed in a part of the power transmitting path betweenthe power distributing mechanism 16 and the output rotary member 22,such that the automatic transmission portion 20 is connected in serieswith the power distributing mechanism 16 through the power transmittingmember 18.

The vehicular drive system 10 is suitably installed transversely on anFF (front-engine front-drive) hybrid vehicle, such that the vehiculardrive system 10 is disposed between a vehicle drive power source in theform of the engine 8 and a pair of drive wheels (front wheels) 38 a, 38b. The output of the engine 8 is transmitted to the drive wheels 38 a,38 b through a final reduction gear device (differential gear unit) 36and a pair of axles 37 a, 37 b. The final reduction gear device 36 isprovided to distribute a torque evenly to the two drive wheels 38 a, 38b while permitting them to rotate at different speeds, and includes: alarge-diameter gear 31 rotatable about a third axis CL3 parallel to thefirst and second axes CL1, CL2; a differential casing 32 rotatable withthe large-diameter gear 31; a pair of differential small gears 34supported by a pin 33 fixed to the differential casing 32perpendicularly to the third axis CL3, such that the differential smallgears 34 are rotatable about an axis of the pin 33; and a pair ofdifferential large gears 35 a, 35 b which are fixed to the respectiveaxes 37 a, 37 b and which mesh with the respective differential smallgears 34.

The power distributing mechanism 16 is a mechanism arranged tomechanically distribute the output of the engine 8 to the first electricmotor M1 and the power transmitting member 18, and to mechanicallysynthesize the output of the engine 8 and the output of the firstelectric motor M1 into a drive force to be transmitted to the powertransmitting member 18. In the present embodiment, the first and secondelectric motors M1, M2 have respective stators M1 s, M2 s, andrespective rotors M1 r, M2 r, and each of these motors M1, M2 is aso-called motor/generator operable also as an electric generator.However, the first electric motor M1 is required to function as anelectric generator capable of generating a reaction force, but need notbe operated to generate a vehicle drive force, while the second electricmotor M2 is required to function as a vehicle drive motor operable togenerate a vehicle drive force, but need not be operated as an electricgenerator.

The power distributing mechanism 16 includes a first planetary gear set24 of single pinion type having a gear ratio ρ1 of about 0.418, forexample, and is switchable by the switching clutch C0 and the switchingbrake B0, between a selected one of a differential state and anon-differential state. The first planetary gear set 24 has rotaryelements consisting of a first sun gear S1, a first planetary gear. P1;a first carrier CA1 supporting the first planetary gear P1 such that thefirst planetary gear P1 is rotatable about its axis and about the axisof the first sun gear S1; and a first ring gear R1 meshing with thefirst sun gear S1 through the first planetary gear P1. Where the numbersof teeth of the first sun gear S1 and the first ring gear R1 arerepresented by ZS1 and ZR1, respectively, the above-indicated gear ratioρ1 is represented by ZS1/ZR1.

In the power distributing mechanism 16, the first carrier CA1 isconnected to the input rotary shaft 14, that is, to the engine 8, andthe first sun gear S1 is connected to the rotor M1 r of the firstelectric motor M1, while the first ring gear R1 and the rotor M2 r ofthe second electric motor M2 are connected to the power transmittingmember 18. The switching brake B0 is disposed between the first sun gearS1 and the housing 12, and the switching clutch C0 is disposed betweenthe first sun gear S1 and the first carrier CA1. When the switchingclutch C0 and brake B0 are both released, the power distributingmechanism 16 is placed in the differential state in which the first sungear S1, first carrier CA1 and first ring gear R1 are rotatable relativeto each other, so as to perform a differential function, so that theoutput of the engine 8 is distributed to the first electric motor M1 andthe power transmitting member 18, whereby a portion of the output of theengine 8 which is distributed to the first electric motor M1 is used todrive the first electric motor M1 to generate an electric energy whichis stored or used to drive the second electric motor M2. Accordingly,the power distributing mechanism 16 is placed in a continuously-variableshifting state in which the rotating speed of the power transmittingmember 18 is continuously variable, irrespective of the rotating speedof the engine 8, namely, in the differential state orcontinuously-variable shifting state in which the power distributingmechanism 16 functions as an electrically controlled continuouslyvariable transmission whose speed ratio γ0 (rotating speed of the inputrotary member 14/rotating speed of the power transmitting member 18) iscontinuously variable from a minimum value γ0min to a maximum valueγ0max.

When the switching clutch C0 is engaged during running of the vehicle bythe output of the engine 8 while the power distributing mechanism 16 isplaced in the continuously-variable shifting state, the first sun gearS1 and the first carrier CA1 are connected together, so that the powerdistributing mechanism 16 is brought into the non-differential state,namely, in the locked state in which the three rotary elements of thefirst planetary gear set 24 consisting of the first sun gear S1, firstcarrier CA1 and first ring gear R1 are rotatable as a unit. In thisnon-differential state in which the rotating speed of the engine 8 andthe rotating speed of the power transmitting member 18 are made equal toeach other, the power distributing mechanism is placed in afixed-speed-ratio shifting state in which the power distributingmechanism 16 functions as a transmission having a fixed speed ratio γ0equal to 1. When the switching brake B0 is engaged in place of theswitching clutch C0, the power distributing mechanism 16 is placed inthe non-differential or locked state in which the first sun gear S1 isnot rotatable, so that the rotating speed of the first ring gear R1 ismade higher than that of the first carrier CA1, whereby the powerdistributing mechanism 16 is placed in the fixed-speed-ratio shiftingstate in which the power distributing mechanism 16 functions as aspeed-increasing transmission having a fixed speed ratio γ0 smaller than1, for example, about 0.7. In the present embodiment described above,the switching clutch C0 and brake B0 function as a differential-stateswitching operable to selectively place the power distributing mechanism16 in the differential state (continuously-variable shifting state) inwhich the power distributing mechanism 16 functions as an electricallycontrolled continuously variable transmission the speed ratio of whichis continuously variable, and in the non-differential state, namely, inthe locked state in which the first planetary gear set 24 does notfunction as the electrically controlled continuously variabletransmission having the continuously-variable shifting function, thatis, in the fixed-speed-ratio shifting state in which the first planetarygear set 24 functions as a transmission having a single gear positionwith one speed ratio or a plurality of gear positions with respectivespeed ratios. As described above, the switching clutch C0 and theswitching brake B0 also function as the hydraulically operateddifferential limiting device operable to limit the differential functionof the power distributing mechanism 16, that is, the differentialfunction of the first planetary gear set 24.

The drive gear 19 is fixed to one of opposite axial end portions of thepower transmitting member 18, which is remote from the engine 8, whilethe driven gear 21 meshing with the drive gear 19 is fixed to one axialend portion of a first intermediate shaft 40, so that a rotary motion ofthe power transmitting member 18 is transmitted to the automatictransmission portion 20 through the first intermediate shaft 40. Theautomatic transmission portion 20 is provided with a first clutch C1through which a rotary motion of the first intermediate shaft 40 istransmitted to a second intermediate shaft 42, and a second clutch C2through which the rotary motion of the first intermediate shaft 40 istransmitted to a tubular sun gear shaft 114.

The automatic transmission portion 20 includes a plurality ofhydraulically operated frictional coupling devices, and a plurality ofplanetary gear sets which are a single-pinion type second planetary gearset 26, a single-pinion type third planetary gear set 28 and asingle-pinion type fourth planetary gear set 30. The second planetarygear set 26 has: a second sun gear S2; a second planetary gear P2; asecond carrier CA2 supporting the second planetary gear P2 such that thesecond planetary gear P2 is rotatable about its axis and about the axisof the second sun gear S2; and a second ring gear R2 meshing with thesecond sun gear S2 through the second planetary gear P2. For example,the second planetary gear set 26 has a gear ratio ρ2 of about 0.562. Thethird planetary gear set 28 has: a third sun gear S3; a third planetarygear P3; a third carrier CA3 supporting the third planetary gear P3 suchthat the third planetary gear P3 is rotatable about its axis and aboutthe axis of the third sun gear S3; and a third ring gear R3 meshing withthe third sun gear S3 through the third planetary gear P3. For example,the third planetary gear set 28 has a gear ratio ρ3 of about 0.425. Thefourth planetary gear set 30 has: a fourth sun gear S4; a fourthplanetary gear P4; a fourth carrier CA4 supporting the fourth planetarygear P4 such that the fourth planetary gear P4 is rotatable about itsaxis and about the axis of the fourth sun gear S4; and a fourth ringgear R4 meshing with the fourth sun gear S4 through the fourth planetarygear P4. For example, the fourth planetary gear set 30 has a gear ratioρ4 of about 0.424. Where the numbers of teeth of the second sun gear S2,second ring gear R2, third sun gear S3, third ring gear R3, fourth sungear S4 and fourth ring gear r4 are represented by ZS2, ZR2, ZS3, ZR3,ZS4 and ZR4, respectively, the above-indicated gear ratios ρ2, ρ3 and ρ4are represented by ZS2/ZR2. ZS3/ZR3, and ZS4/ZR4, respectively. The sungears S, ring gears R and planetary gears P are all helical gears.

In the automatic transmission portion 20, the second sun gear S2 and thethird sun gear S3 are integrally fixed to each other as a unit,selectively connected to the power transmitting member 18 through theabove-indicated second clutch C2, and selectively fixed to the housing12 through a first brake B1. The second carrier CA2 is selectively fixedto the housing 12 through a second brake B2, and the fourth ring gear R4is selectively fixed to the housing 12 through a third brake B3, whilethe second ring gear R2, third carrier CA3 and fourth carrier CA4 areintegrally fixed to each other and fixed to the output rotary member 22.The third ring gear R3 and the fourth sun gear S4 are integrally fixedto each other and selectively connected to the power transmitting member18 through the above-indicated first clutch C1.

The above-described switching clutch C0, first clutch C1, second clutchC2, switching brake B0, first brake B1, second brake B2 and third brakeB3 are hydraulically operated frictional coupling devices used in aconventional vehicular automatic transmission. Each of these frictionalcoupling devices except the first brake B1 is constituted by a wet-typemultiple-disc coupling device including a plurality of friction plateswhich are superposed on each other and which are forced against eachother by a hydraulic actuator. The first brake B1 is a band brakeincluding a rotary drum and one band or two bands which is/are wound onthe outer circumferential surface of the rotary drum and tightened atone end by a hydraulic actuator.

In the drive system 10 constructed as described above, one of a firstgear position (first speed position) through a fifth gear position(fifth speed position), a reverse gear position (rear drive position)and a neural position is selectively established by engaging actions ofa corresponding combination of the frictional coupling devices selectedfrom the above-described switching clutch C0, first clutch C1, secondclutch C2, switching brake B0, first brake B1, second brake B2 and thirdbrake B3, as indicated in the table of FIG. 2. Those gear positions haverespective speed ratios γ (input shaft speed N_(IN)/output shaft speedN_(OUT)) which change as geometric series. In particular, it is notedthat the power distributing mechanism 16 is provided with the switchingclutch C0 and brake B0, so that the power distributing mechanism 16 canbe selectively placed by engagement of the switching clutch C0 orswitching brake B0, in the fixed-speed-ratio shifting state in which thepower distributing mechanism 16 is operable as a transmission having asingle gear position with one speed ratio or a plurality of gearpositions with respective speed ratios, as well as in thecontinuously-variable shifting state in which the power distributingmechanism 16 is operable as a continuously variable transmission, asdescribed above. In the present vehicular drive system 10, therefore, astep-variable transmission is constituted by the automatic transmissionportion 20, and the power distributing mechanism 16 which is placed inthe fixed-speed-ratio shifting state by engagement of the switchingclutch C0 or switching brake B0. Further, a continuously variabletransmission is constituted by the automatic transmission portion 20,and the power distributing mechanism 16 which is placed in thecontinuously-variable shifting state, with none of the switching clutchC0 and brake B0 being engaged.

Where the drive system 10 functions as the step-variable transmission,for example, the first gear position having the highest speed ratio γ1of about 3.357, for example, is established by engaging actions of theswitching clutch C0, first clutch C1 and third brake B3, and the secondgear position having the speed ratio γ2 of about 2.180, for example,which is lower than the speed ratio γ1, is established by engagingactions of the switching clutch C0, first clutch C1 and second brake B2,as indicated in FIG. 2. Further, the third gear position having thespeed ratio γ3 of about 1.424, for example, which is lower than thespeed ratio γ2, is established by engaging actions of the switchingclutch C0, first clutch C1 and first brake B1, and the fourth gearposition having the speed ratio γ4 of about 1.000, for example, which islower than the speed ratio γ3, is established by engaging actions of theswitching clutch C0, first clutch C1 and second clutch C2. The fifthgear position having the speed ratio γ5 of about 0705, for example,which is smaller than the speed ratio γ4, is established by engagingactions of the first clutch C1, second clutch C2 and switching brake B0.Further, the reverse gear position having the speed ratio γR of about3.209, for example, which is intermediate between the speed ratios γ1and γ2, is established by engaging actions of the second clutch C2 andthe third brake B3. The neutral position N is established by engagingonly the switching clutch C0.

Where the drive system 10 functions as the continuously-variabletransmission, on the other hand, the switching clutch C0 and theswitching brake B0 are both released, as indicated in FIG. 2, so thatthe power distributing mechanism 16 functions as the continuouslyvariable transmission, while the automatic transmission portion 20connected in series to the power distributing mechanism 16 functions asthe step-variable transmission, whereby the speed of the rotary motiontransmitted to the automatic transmission portion 20 placed in one ofthe first, second, third and fourth gear positions, namely, the rotatingspeed of the power transmitting member 18 is continuously changed, sothat the speed ratio when the automatic transmission portion 20 isplaced in one of those gear positions is continuously variable over apredetermined range. Accordingly, the speed ratio of the automatictransmission portion 20 is continuously variable across the adjacentgear positions, whereby the overall speed ratio γT of the drive system10 is continuously variable.

The collinear chart of FIG. 3 indicates, by straight lines, arelationship among the rotating speeds of the rotary elements in each ofthe gear positions of the drive system 10, which is constituted by thepower distributing mechanism 16 functioning as the continuously-variableshifting portion or first shifting portion, and the automatictransmission portion 20 functioning as the step-variable shiftingportion or second shifting portion. The collinear chart of FIG. 3 is arectangular two-dimensional coordinate system in which the gear ratios ρof the planetary gear sets 24, 26, 28, 30 are taken along the horizontalaxis, while the relative rotating speeds of the rotary elements aretaken along the vertical axis. A lower one of three horizontal lines X1,X2, XG, that is, the horizontal line X1 indicates the rotating speed of0, while an upper one of the three horizontal lines, that is, thehorizontal line X2 indicates the rotating speed of 1.0, that is, anoperating speed N_(E) of the engine 8 connected to the input shaft 14.The horizontal line XG indicates the rotating speed of the powertransmitting member 18. Three vertical lines Y1, Y2 and Y3 correspond tothree elements of the power distributing mechanism 16, and respectivelyrepresent the relative rotating speeds of a second rotary element(second element) RE2 in the form of the first sun gear S1, a firstrotary element (first element) RE1 in the form of the first carrier CA1,and a third rotary element (third element) RE3 in the form of the firstring gear R1. The distances between the adjacent ones of the verticallines Y1, Y2 and Y3 are determined by the gear ratio ρ1 of the firstplanetary gear set 24. That is, the distance between the vertical linesY1 and Y2 corresponds to “1”, while the distance between the verticallines Y2 and Y3 corresponds to the gear ratio ρ1. Further, five verticallines Y4, Y5, Y6, Y7 and Y8 corresponding to the automatic transmissionportion 20 respectively represent the relative rotating speeds of afourth rotary element (fourth element) RE4 in the form of the second andthird sun gears S2, S3 integrally fixed to each other, a fifth rotaryelement (fifth element) RE5 in the form of the second carrier CA2, asixth rotary element (sixth element) RE6 in the form of the fourth ringgear R4, a seventh rotary element (seventh element) RE7 in the form ofthe second ring gear R2 and third and fourth carriers CA3, CA4 that areintegrally fixed to each other, and an eighth rotary element (eighthelement) RE8 in the form of the third ring gear R3 and fourth sun gearS4 integrally fixed to each other. The distances between the adjacentones of the vertical lines Y4-Y8 are determined by the gear ratios ρ2,ρ3 and ρ4 of the second, third and fourth planetary gear sets 26, 28,30. Therefore, as shown in FIG. 3, the distance between the verticallines corresponding to the sun gear and carrier of each of the second,third and fourth planetary gear sets 26, 28, 30 corresponds to “1”,while the distance between the vertical lines corresponding to thecarrier and ring gear corresponds to the gear ratio ρ.

Referring to the collinear chart of FIG. 3, the power distributingmechanism 16 (continuously-variable transmission portion) of the drivesystem 10 is arranged such that the first rotary element RE1 (firstcarrier CA1) of the first planetary gear set 24, is integrally fixed tothe input rotary member 14, that is, to the engine 8, and is selectivelyconnected to the second rotary element RE2 (first sun gear S1) throughthe switching clutch C0, and this rotary element RE2 is connected to thefirst electric motor M1 and selectively fixed to the housing 12 throughthe switching brake B0, while the third rotary element RE3 (first ringgear R1) is fixed to the power transmitting member 18 and connected tothe second electric motor M2, so that a rotary motion of thedifferential mechanism input rotary member 14 is transmitted to theautomatic transmission (step-variable transmission portion) 20 throughthe power transmitting member 18. A relationship between the rotatingspeeds of the first sun gear S1 and the first ring gear R1 isrepresented by an inclined straight line L0 which passes a point ofintersection between the lines Y2 and X2.

FIGS. 4 and 5 correspond to a part of the collinear chart of FIG. 3which shows the power distributing mechanism 16. FIG. 4 shows an exampleof an operating state of the power distributing mechanism 16 placed inthe continuously-variable shifting state with the switching clutch C0and the switching brake B0 held in the released state. The rotatingspeed of the first sun gear S1 represented by the point of intersectionbetween the straight line L0 and vertical line Y1 is raised or loweredby controlling the reaction force generated by an operation of the firstelectric motor M1 to generate an electric energy, so that the rotatingspeed of the first ring gear R1 represented by the point of intersectionbetween the lines L0 and Y3 is lowered or raised.

FIG. 5 shows an operating state of the power distributing mechanism 16placed in the step-variable shifting state with the switching clutch C0held in the engaged state. When the first sun gear S1 and the firstcarrier CA1 are connected to each other, the three rotary elementsindicated above are rotated as a unit, so that the straight line L0 isaligned with the horizontal line X2, whereby the power transmittingmember 18 is rotated at a speed equal to the engine speed N_(E). Whenthe switching brake B0 is engaged, on the other hand, the rotation ofthe first sun gear S1 is stopped, so that the straight line L0 isinclined in the state indicated in FIG. 3, whereby the rotating speed ofthe first ring gear R1, that is, the rotation of the power transmittingmember 18 represented by a point of intersection between the lines L0and Y3 is made higher than the engine speed N_(E) and transmitted to theautomatic transmission portion 20.

In the automatic transmission portion 20, the fourth rotary element RE4is selectively connected to the power transmitting member 18 through thesecond clutch C2, and selectively fixed to the housing 12 through thefirst brake B1, and the fifth rotary element RE5 is selectively fixed tothe housing 12 through the second brake B2, while the sixth rotaryelement RE6 is selectively fixed to the housing 12 through the thirdbrake B3. The seventh rotary element RE7 is integrally fixed to thedrive system output rotary member 22, while the eighth rotary elementRE8 is selectively connected to the power transmitting member 18 throughthe first clutch C1.

When the first clutch C1 and the third brake B3 are engaged, theautomatic transmission portion 20 is placed in the first gear position.The rotating speed of the drive system output rotary member 22 in thefirst gear position is represented by a point of intersection betweenthe vertical line Y7 indicative of the rotating speed of the seventhrotary element RE7 fixed to the drive system output rotary member 22 andan inclined straight line L1 which passes a point of intersectionbetween the vertical line Y8 indicative of the rotating speed of theeighth rotary element RE8 and the horizontal line X2, and a point ofintersection between the vertical line Y6 indicative of the rotatingspeed of the sixth rotary element RE6 and the horizontal line X1.Similarly, the rotating speed of the output rotary member 22 in thesecond gear position established by the engaging actions of the firstclutch C1 and second brake B2 is represented by a point of intersectionbetween an inclined straight line L2 determined by those engagingactions and the vertical line Y7 indicative of the rotating speed of theseventh rotary element RE7 fixed to the output rotary member 22. Therotating speed of the output rotary member 22 in the third gear positionestablished by the engaging actions of the first clutch C1 and firstbrake B1 is represented by a point of intersection between an inclinedstraight line L3 determined by those engaging actions and the verticalline Y7 indicative of the rotating speed of the seventh rotary elementRE7 fixed to the output rotary member 22. The rotating speed of theoutput rotary member 22 in the fourth gear position established by theengaging actions of the first clutch C1 and second clutch C2 isrepresented by a point of intersection between a horizontal line L4determined by those engaging actions and the vertical line Y7 indicativeof the rotating speed of the seventh rotary element RE7 fixed to theoutput rotary member 22. In the first-speed through fourth gearpositions in which the switching clutch C0 is placed in the engagedstate, the eighth rotary element RE8 is rotated at the same speed as theengine speed N_(E), with the drive force received from the powerdistributing mechanism 16, that is, from the power distributingmechanism 16. When the switching brake B0 is engaged in place of theswitching clutch C0, the eighth rotary element RE8 is rotated at a speedhigher than the engine speed N_(E), with the drive force received fromthe power distributing mechanism 16. The rotating speed of the outputrotary member 22 in the fifth gear position established by the engagingactions of the first clutch C1, second clutch C2 and switching brake B0is represented by a point of intersection between a horizontal line L5determined by those engaging actions and the vertical line Y7 indicativeof the rotating speed of the seventh rotary element RE7 fixed to theoutput rotary member 22. The rotating speed of the output rotary member22 in the reverse gear position established by the engaging actions ofthe second clutch C2 and the third brake B3 is represented by a point ofintersection between an inclined straight line LR and the vertical lineY7.

FIG. 6 illustrates signals received by an electronic control device 50provided to control the drive system 10, and signals generated by theelectronic control device 50. This electronic control device 50 includesa so-called microcomputer incorporating a CPU, a ROM, a RAM and aninput/output interface, and is arranged to process the signals accordingto programs stored in the ROM while utilizing a temporary data storagefunction of the ROM, to implement hybrid drive controls of the engine 8and electric motors M1 and M2, and drive controls such as a shiftingcontrol of the automatic transmission portion 20.

The electronic control device 50 is arranged to receive, from varioussensors and switches shown in FIG. 6, various signals such as: a signalindicative of a temperature of cooling water of the engine; a signalindicative of a selected operating position of a shift lever 58; asignal indicative of the operating speed N_(E) of the engine 8; a signalindicative of a value indicating a selected group of forward-drivepositions of the transmission mechanism; a signal indicative of an Mmode (motor-drive mode); a signal indicative of an operated state of anair conditioner; a signal indicative of a vehicle speed corresponding tothe rotating speed of the output rotary member 22; a signal indicativeof a temperature of a working oil of the automatic transmission portion20; a signal indicative of an operated state of a side brake; a signalindicative of an operated state of a foot brake; a signal indicative ofa temperature of a catalyst; a signal indicative of an operating amountof an accelerator pedal; a signal indicative of an angle of a cam; asignal indicative of the selection of a snow drive mode; a signalindicative of a longitudinal acceleration value of the vehicle; a signalindicative of the selection of an auto-cruising drive mode; a signalindicative of a weight of the vehicle; signals indicative of speeds ofthe drive wheels of the vehicle; a signal indicative of an operatingstate of a step-variable shifting switch provided to place the powerdistributing mechanism 16 in the fixed-speed-ratio shifting state inwhich the drive system 10 functions as a step-variable transmission; asignal indicative of a continuously-variable shifting switch provided toplace the power distributing mechanism 16 in the continuouslyvariable-shifting state in which the drive system 10 functions as thecontinuously variable transmission; a signal indicative of a rotatingspeed N_(M1) of the first electric motor M1; and a signal indicative ofa rotating speed N_(M2) of the second electric motor M2. The electroniccontrol device 50 is further arranged to generate various signals suchas: a signal to drive an electronic throttle actuator for controlling anangle of opening of a throttle valve; a signal to adjust a pressure of asupercharger; a signal to operate the electric air conditioner; a signalfor controlling an ignition timing of the engine 8; signals to operatethe electric motors M1 and M2; a signal to operate a shift-rangeindicator for indicating the selected operating position of the shiftlever; a signal to operate a gear-ratio indicator for indicating thegear ratio; a signal to operate a snow-mode indicator for indicating theselection of the snow drive mode; a signal to operate an ABS actuatorfor anti-lock braking of the wheels; a signal to operate an M-modeindicator for indicating the selection of the M-mode; signals to operatesolenoid-operated valves incorporated in a hydraulic control unit 42provided to control the hydraulic actuators of the hydraulicallyoperated frictional coupling devices of the power distributing mechanism16 and the automatic transmission portion 20; a signal to operate anelectric oil pump used as a hydraulic pressure source for the hydrauliccontrol unit 42; a signal to drive an electric heater; and a signal tobe applied to a cruise-control computer.

FIG. 7 is a functional block diagram illustrating major controlfunctions performed by the electronic control device 50. Switchingcontrol means 60 is arranged to determine whether the vehicle conditionis in a continuously-variable shifting region in which the drive system10 should be placed in the continuously-variable shifting state, or in astep-variable shifting region in which the drive system 10 should beplaced in the step-variable shifting state. This determination is madeon the basis of a stored predetermined relationship shown in FIG. 8 or9, for example. Where the relationship shown in FIG. 8 (switchingboundary line map) is used, the determination is made on the basis ofthe vehicle condition as represented by the actual engine speed N_(E),and a drive-force-related value relating to the drive force of thehybrid vehicle, for example, an engine output torque T_(E).

According to the relationship shown in FIG. 8, the step-variableshifting region is set to be a high-torque region (a high-output runningregion in which the output torque T_(E) of the engine 8 is not lowerthan a predetermined value TE1, or a high-speed region in which theengine speed N_(E) is not lower than a predetermined value NE1, namely,a high-vehicle-speed region in which the vehicle speed which is one ofthe vehicle conditions and which is determined by the engine speed NEand the overall speed ratio γT is not lower than a predetermined value,or a high-output region in which the vehicle output calculated from theoutput torque T_(E) and speed N_(E) of the engine 8 is not lower than apredetermined value. Accordingly, the step-variable shifting control iseffected when the vehicle is running with a comparatively high outputtorque or speed of the engine 8, or with a comparatively high vehicleoutput. The step-variable shifting control permits a change of theengine speed N_(E) as a result of a shift-up action of the transmission,that is, a rhythmic change of the speed of the engine 8. Namely, thecontinuously-variable shifting state is switched to the step-variableshifting state (fixed-speed-ratio shifting state) when the vehicle isplaced in a high-output running state in which a desire of the vehicleoperator to increase the vehicle drive force should be satisfied rathera desired to improve the fuel economy. Accordingly, the vehicle operatorcan enjoy a comfortable rhythmic change of the engine speed N_(E). Onthe other hand, the continuously-variable shifting control is effectedwhen the vehicle is running with a comparatively low output torque orspeed of the engine 8, or with a comparatively low vehicle output, thatis, when the engine 8 is a normal output state. A boundary line definingthe step-variable shifting region and the continuously-variable shiftingregion in FIG. 8 corresponds to a high-vehicle speed determining linedefined by a series of high-vehicle-speed upper limit values, or ahigh-output running determining line defined by a series of high-outputupper limit values.

When the relationship shown in FIG. 9 is used, the above-indicateddetermination is made on the basis of the actual vehicle speed V and thedrive-force-related value in the form of the output torque T_(OUT). InFIG. 9, a broken line indicates a threshold vehicle speed V1 and athreshold output torque T1 which define a predetermined vehiclecondition used for switching from the continuously-variable shiftingcontrol to the step-variable shifting control, and two-dot chain lineindicates a predetermined vehicle condition used for switching from thestep-variable shifting control to the continuously-variable shiftingcontrol. Thus, there is provided a hysteresis for determination as towhether the shifting state should be switched between the step-variableshifting region and the continuously-variable shifting region. In FIG.9, a solid line 51 indicates a boundary line defining a motor driveregion in which the vehicle is driven by a drive force generated by theelectric motor, with a relatively low vehicle output torque or at arelatively low vehicle speed. FIG. 9 also shows a shift boundary datamap which uses control parameters in the form of the vehicle speed V andthe output torque _(TOUT).

When the switching control means 60 determines that the vehiclecondition is in the step-variable shifting region, the switching controlmeans 60 disables a hybrid control means 62 to effect a hybrid controlor continuously-variable shifting control, and enables a step-variableshifting control means 64 to effect a predetermined step-variableshifting control. Where the step-variable shifting control means 64effects the step-variable shifting control according to thedetermination made on the basis of the relationship of FIG. 8, thestep-variable shifting control means 64 effects an automatic shiftingcontrol according to a stored predetermined shift boundary data map.Where the determination is made on the basis of the relationship of FIG.9, the automatic shifting control is effected according to the shiftboundary data map shown in FIG. 9.

FIG. 2 indicates the combinations of the operating states of thehydraulically operated frictional coupling devices C0, C1, C2, B0, B1,B2 and B3, which are selectively engaged for effecting the step-variableshifting control. In this automatic step-variable shifting control mode,the first through fourth gear positions are established by an engagingaction of the switching clutch C0, and the power distributing mechanism16 functions as an auxiliary transmission having a fixed speed ratio ofγ0 equal to “1”. On the other hand, the fifth gear position isestablished by an engaging action of the switching brake B0 in place ofthe switching clutch C0, and the power distributing mechanism 16functions as an auxiliary transmission having a fixed speed ratio γ0equal to about 0.7, for example. That is, the drive system 10 as a wholeincluding the power distributing mechanism 16 functioning as theauxiliary transmission and the automatic transmission portion 20functions as a so-called “automatic transmission”, in the automaticstep-variable shifting control mode.

The drive-force-related value indicated above is a parametercorresponding to the drive force of the vehicle, which may be the outputtorque T_(OUT) of the automatic transmission portion 20, the outputtorque T_(E) of the engine 8, or the acceleration value of the vehicle,as well as the drive torque or drive force of drive wheels 38. Theengine output torque T_(E) may be an actual value calculated on thebasis of the operating angle of the accelerator pedal or the openingangle of the throttle valve (or intake air quantity, air/fuel ratio oramount of fuel injection) and the engine speed N_(E), or an estimatedvalue of the required vehicle drive force which is calculated on thebasis of the amount of operation of the accelerator pedal by the vehicleoperator or the operating angle of the throttle valve. The vehicle drivetorque may be calculated on the basis of not only the output torqueT_(OUT), etc., but also the ratio of a differential gear device and theradius of the drive wheels 38, or may be directly detected by a torquesensor or the like.

When the switching control means 60 determines that the vehiclecondition is in the continuously-variable shifting region, on the otherhand, the switching control means 60 commands the hydraulic control unit42 to release both of the switching clutch C0 and the switching brake B0for placing the power distributing mechanism 16 in the electricallyestablished continuously-variable shifting state. At the same time, theswitching control means 60 enables the hybrid control means 62 to effectthe hybrid control, and commands the step-variable shifting controlmeans 64 to select and hold a predetermined one of the gear positions,or to permit an automatic shifting control according to the storedpredetermined shift boundary data map. In the latter case, thevariable-step shifting control means 64 effects the automatic shiftingcontrol by suitably selecting the combinations of the operating statesof the frictional coupling devices indicated in the table of FIG. 2,except the combinations including the engagement of the switching clutchC0 and brake B0. Thus, the power distributing mechanism 16 placed in thecontinuously-variable shifting state under the control of the switchingcontrol means 60 functions as the continuously variable transmissionwhile the automatic transmission portion 20 connected in series to thepower distributing mechanism 16 functions as the step-variabletransmission, so that the drive system provides a sufficient vehicledrive force, such that the speed of the rotary motion transmitted to theautomatic transmission portion 20 placed in one of the first, second,third and fourth gear positions, namely, the rotating speed of the powertransmitting member 18 is continuously changed, so that the speed ratioof the drive system when the automatic transmission portion 20 is placedin one of those gear positions is continuously variable over apredetermined range. Accordingly, the speed ratio of the automatictransmission portion 20 is continuously variable through the adjacentgear positions, whereby the overall speed ratio γT of the drive system10 as a whole is continuously variable.

The hybrid control means 62 controls the engine 8 to be operated withhigh efficiency, so as to establish an optimum proportion of the driveforces which are produced by the engine 8, and the first electric motorM1 and/or the second electric motor M2. For instance, the hybrid controlmeans 62 calculates the output as required by the vehicle operator atthe present running speed V of the vehicle, on the basis of theoperating amount of the accelerator pedal and the vehicle running speed,and calculate a required vehicle drive force on the basis of thecalculated required output and a required amount of generation of anelectric energy to be stored. On the basis of the calculated requiredvehicle drive force, the hybrid control means 62 calculates a desiredengine speed and a desired total output, and controls the actual outputof the engine 8 and the amount of generation of the electric energy bythe first electric motor M1, according to the calculated desired totaloutput and engine speed N_(E). The hybrid control means 62 is arrangedto control the shifting action of the automatic transmission portion 20,while taking account of the presently selected gear position of theautomatic transmission portion 20, so as to improve the fuel economy ofthe engine 8. In the hybrid control, the power distributing mechanism 16is controlled to function as the electrically controlledcontinuously-variable transmission, for optimum coordination of theengine speed N_(E) and vehicle speed V for efficient operation of theengine 8, and the rotating speed of the power transmitting member 18determined by the selected gear position of the automatic transmissionportion 20. That is, the hybrid control means 62 determines a targetvalue of the overall speed ratio γT of the transmission mechanism 10 sothat the engine 8 is operated according a stored highest-fuel-economycurve that satisfies both of the desired operating efficiency and thehighest fuel economy of the engine 8. The hybrid control means 62controls the speed ratio γ0 of the differential portion 11, so as toobtain the target value of the overall speed ratio γT, so that theoverall speed ratio γT can be controlled within a predetermined range,for example, between 13 and 0.5.

The hybrid control means 62 controls an inverter 68 such that theelectric energy generated by the first electric motor M1 is supplied toan electric-energy storage device 70 and the second electric motor M2through the inverter 68. That is, a major portion of the drive forceproduced by the engine 8 is mechanically transmitted to the powertransmitting member 18, while the remaining portion of the drive forceis consumed by the first electric motor M1 to convert this portion intothe electric energy, which is supplied from the first electric motor M1to the second electric motor M2 through the inverter 68 and consumed bythe second electric motor M2, or supplied from the first electric motorM1 to the electric-energy storage device 70 through the inverter 68 andsubsequently consumed by the first electric motor M1. A drive forceproduced by an operation of the second electric motor M2 or firstelectric motor M1 with the electric energy generated by the firstelectric motor M1 is transmitted to the power transmitting member 18.Thus, the transmission mechanism 10 is provided with an electric paththrough which an electric energy generated by conversion of a portion ofa drive force of the engine 8 is converted into a mechanical energy.This electric path includes components associated with the generation ofthe electric energy and the consumption of the generated electric energyby the second electric motor M2. The hybrid control means 62 canestablish a motor-drive mode to drive the vehicle by utilizing theelectric CVT function of the power distributing mechanism 16,irrespective of whether the engine 8 is in the non-operated state or inthe idling state.

In the above-described arrangements of the switching control means 60,hybrid control means 62 and step-variable shifting control means 64, thepower distributing mechanism 16 is placed in the continuously-variableshifting state, assuring a high degree of fuel economy of the vehicle,when the vehicle is in a low- or medium-speed running state or in a low-or medium-output running state, with the engine operated in the normaloutput state. When the vehicle is in a high-speed running state or at ahigh speed of operation of the engine 8, on the other hand, the powerdistributing mechanism 16 is placed in the fixed-speed-ratio shiftingstate in which the output of the engine 8 is transmitted to the drivewheels 38 primarily through the mechanical power transmitting path, sothat the fuel economy is improved owing to reduction of a loss ofconversion of the mechanical energy into the electric energy. When theengine 8 is in a high-output state, the power distributing mechanism 16is placed in the fixed-speed-ratio shifting state. Thus, the powerdistributing mechanism 16 is placed in the continuously-variableshifting state, only when the vehicle speed or output is relatively lowor medium, so that the required amount of electric energy generated bythe first electric motor M1, that is, the maximum amount of electricenergy that must be transmitted from the first electric motor M1 can bereduced, whereby the required electrical reaction force of the firstelectric motor M1 can be reduced, making it possible to minimize therequired sizes of the first and second electric motors M1, M2, and therequired size of the drive system 10 including the electric motors.

FIG. 10 shows an example of a manually operable shifting device in theform of a shifting device 56. The shifting device 56 includes theabove-described shift lever 58, which is disposed laterally adjacent toan operator's seat, for example, and which is manually operated toselect one of a plurality of positions consisting of: a parking positionP for placing the drive system 10 (namely, automatic transmissionportion 20) in a neutral state in which a power transmitting path isdisconnected with both of the switching clutch C0 and brake B0 placed inthe released state, and at the same time the output rotary member 22 ofthe automatic transmission portion 20 is in the locked state; areverse-drive position R for driving the vehicle in the rearwarddirection; a neutral position N for placing the drive system 10 in theneutral state; an automatic forward-drive shifting position D; and amanual forward-drive shifting position M. The parking position P and theneutral position N are non-driving positions selected when the vehicleis not driven, while the reverse-drive position R, and the automatic andmanual forward-drive shifting positions D, M are driving positionsselected when the vehicle is driven. The automatic forward-driveshifting position D provides a highest-speed position, and positions “4”through “L” selectable in the manual forward-drive shifting position Mare engine-braking positions in which an engine brake is applied to thevehicle.

The manual forward-drive shifting position M is located at the sameposition as the automatic forward-drive shifting position D in thelongitudinal direction of the vehicle, and is spaced from or adjacent tothe automatic forward-drive shifting position D in the lateral directionof the vehicle. The shift lever 58 is operated to the manualforward-drive shifting position M, for manually selecting one of thepositions “D” through “L”. Described in detail, the shift lever 58 ismovable from the manual forward-drive shifting position M to a shift-upposition “+” and a shift-down position “−”, which are spaced from eachother in the longitudinal direction of the vehicle. Each time the shiftlever 58 is moved to the shift-up position “+” or the shift-downposition “−”, the presently selected position is changed by oneposition. The five positions “D” through “L” have respective differentlower limits of a range in which the overall speed ratio γT of the drivesystem 10 is automatically variable, that is, respective differentlowest values of the overall speed ratio γT which corresponds to thehighest output speed of the drive system 10. Namely, the five positions“D” through “L” select respective different numbers of the gearpositions or speed positions of the automatic transmission portion 20which are automatically selectable, so that the lowest overall speedratio γT available is determined by the selected number of theselectable gear positions. The shift lever 58 is biased by biasing meanssuch as a spring so that the shift lever 58 is automatically returnedfrom the shift-up position “+” and shift-down position “−” back to themanual forward-drive shifting position M. The shifting device 46 isprovided with shift-position sensors operable to detect the presentlyselected position of the shift lever 58, so that signals indicative ofthe presently selected operating position of the shift lever 58 and thenumber of shifting operations of the shift lever 58 in the manualforward-shifting position M are supplied to the electronic controldevice 50.

When the shift lever 56 is operated to the automatic forward-driveshifting position D, the switching control means 60 effects an automaticswitching control of the drive system 10, and the hybrid control means62 effects the continuously-variable shifting control of the powerdistributing mechanism 16, while the step-variable shifting controlmeans 64 effects an automatic shifting control of the automatictransmission portion 20. When the drive system 10 is placed in thestep-variable shifting state, for example, the shifting action of thedrive system 10 is automatically controlled to select an appropriate oneof the first-gear position through the fifth gear position indicated inFIG. 2. When the drive system 10 is placed in the continuously-variableshifting state, the speed ratio of the power distributing mechanism 16is continuously changed, while the shifting action of the automatictransmission portion 20 is automatically controlled to select anappropriate one of the first-gear through fourth gear positions, so thatthe overall speed ratio γT of the drive system 10 is controlled so as tobe continuously variable within the predetermined range. The automaticforward-drive position D is a position selected to establish anautomatic shifting mode (automatic mode) in which the drive system 10 isautomatically shifted.

When the shift lever 68 is operated to the manual forward-drive shiftingposition M, on the other hand, the shifting action of the drive system10 is automatically controlled by the switching control means 60, hybridcontrol means 62 and step-variable shifting control means 54, such thatthe overall speed ratio γT is variable within a predetermined range thelower limit of which is determined by the gear position having thelowest speed ratio, which gear position is determined by the manuallyselected one of the positions “D” through “L”. When the drive system 10is placed in the step-variable shifting state, for example, the shiftingaction of the drive system 10 is automatically controlled within theabove-indicated predetermined range of the overall speed ratio γT. Whenthe drive system 10 is placed in the continuously-variable shiftingstate, the speed ratio of the power distributing mechanism 16 iscontinuously changed, while the shifting action of the automatictransmission portion 20 is automatically controlled to select anappropriate one of the gear positions the number of which is determinedby the manually selected one of the positions “D” through “L”, so thatthe overall speed ratio γT of the drive system 10 is controlled so as tobe continuously variable within the predetermined range. The manualforward-drive position M is a position selected to establish a manualshifting mode (manual mode) in which the selectable gear positions ofthe drive system 10 are manually selected.

Referring to the cross sectional views of FIGS. 11 and 12, there arerespectively shown a part of the vehicular drive system 10 whichincludes the first planetary gear set 24 and the two electric motors M1,M2, and another part of the vehicular drive system 10 which includes thesecond, third and fourth planetary gear sets 26, 28, 30 and the finalreduction gear device 36. In the vehicular drive system 10, the first,second and third axes CL1, CL2, CL3 are positioned relative to eachother, as shown in FIG. 13. The cross sectional view of FIG. 11 is takenin a plane including the first axis CL1, while the cross sectional viewof FIG. 12 is taken in a plane including the second and third axes CL2,CL3. The horizontal direction as seen in FIG. 13 is the longitudinal orrunning direction of the vehicle, and the vertical direction as seen thesame figure is the vertical direction of the vehicle, while thedirection perpendicular to the plane of FIG. 13 (namely, the directionparallel to the axes CL1-CL3) is the transverse or width direction ofthe vehicle. The first and third axes CL1, CL3 are spaced apart fromeach other in the longitudinal direction of the vehicle by a distancedetermined to prevent an interference between the drive gear 19 and thelarge-diameter gear 31, and have substantially the same verticalpositions. The second axis CL2 is located intermediate between the firstand third axes CL1, CL3 in the longitudinal direction, and has a highervertical position than the first and third axes CL1, CL3.

As shown in FIGS. 11 and 12, the housing 12 consists of four separateparts in the form of a cap-shaped first casing portion 12 a, acylindrical second casing portion 12 b, a cylindrical third casingportion 12 c and a cap-shaped fourth casing portion 12 d, which arearranged in the axial direction parallel to the axes CL1-CL3 and whichare fastened together by bolts (not shown) into a fluid-tight housingstructure. The first, second, third and fourth casing portions 12 a, 12b, 12 c, 12 d are light-alloy castings, for instance, formed of aluminumby die casting.

The first casing portion 12 a is also bolted to the engine 8, and fixedto the second casing portion 12 b, so as to close one of opposite axialopenings which is on the side of the engine 8. The second casing portion12 b includes an integral partition wall 80 which divides its interiorspace into a space on the side of the first axis CL1, and a space on theside of the second axis CL2. The second casing portion 12 furtherincludes an integral partition wall 82 which divides its interior spadeinto a space on the side of the engine 8, and a space remote from theengine 8. In the space defined by the first casing portion 12 a and thepartition wall 82 of the second casing portion 12 b, there areaccommodated the first electric motor M1 coaxially with the first axisCL1, a differential drive gear 84 coaxially with the second axis CL2,and the final reduction gear device 36 coaxially with the third axisCL3. The rotor M1 r of the first electric motor M1 is rotatablysupported by the first casing portion 12 a and the partition wall 82 ofthe second casing portion 12 b, via a pair of bearings 86, and thedifferential drive gear 84 is rotatably supported by the first casingportion 12 a and the partition wall 82, via a pair of bearings 88, whilethe differential casing 32 of the final reduction gear device 36 isrotatably supported by the first and second casing portions 12 a, 12 b,via a pair of bearings 90. The differential drive gear 84 consists of anannular outer gear portion 84 a meshing with the large-diameter gear 31,and a shaft portion 84 b which is splined to the inner circumferentialsurface of the outer gear portion 84 a and which supports the outer gearportion 84 a. The large-diameter gear 31 and the outer gear portion 84 aare both helical gears.

The partition wall 80 of the second casing portion 12 b has an axialextension protruding toward the first casing portion 12 a, and dividesthe interior space between the first and second casing portions 12 a, 12b, into a fifth accommodating chamber 89 accommodating the differentialdrive gear 84, and a first accommodating chamber 91 accommodating thefirst electric motor M1. The free or distal end of the extension of thepartition wall 80 and the first casing portion 12 a cooperate to definea gap A which permits a flow of a lubricant from the fifth accommodatingchamber 89 to the first accommodating chamber 91. The gap A may beconsidered to function as a hole formed through the partition wall 80,for communication between the fifth accommodating chamber 89 and thefirst accommodating chamber 91.

The power distributing mechanism 16 is accommodated coaxially with thefirst axis CL1, in one of the four spaces provided in the second casingportion 12 b and defined by the two partition walls 80, 82, which onespace is on the side of the first axis CL1 and on the side remote fromthe engine 8.

The third casing portion 12 c includes an integral partition wall 92located adjacent to the partition wall 80 in the axial direction, and anintegral support wall 98, and is provided with a separate support wall96 removably fixed thereto by bolts 94. The partition wall 92 and thesupport walls 96, 98 cooperate to define a space in the form of a secondaccommodating chamber 100 in which the second electric motor M2 isaccommodated coaxially with the first axis CL1. The support wall 96defines one of opposite axial ends of the second accommodating chamber100 which is on the side of the engine 8, while the support wall 98defines the other axial end of the second accommodating chamber 100which is remote from the engine 8. The rotor M2 r of the second electricmotor M2 is rotatably supported by the support walls 96, 98, via a pairof bearings 102.

The third casing portion 12 c is further provided with a separatesupport member 104 in the form of a circular disk fitted therein andbolted thereto, so as to define one of opposite axial ends of the spaceprovided in the third casing portion 12 c and located on the side of thesecond axis CL2, which one axial end is remote from the engine 8. Thissupport member 104 functions as a support member for rotatablysupporting the first intermediate shaft 40 and the second intermediateshaft 42, and is fixed removably to the third casing portion 12 c bybolts (not shown). The support member 104 of the third casing portion 12c and the support wall 82 of the second casing portion 12 b cooperate todefine opposite axial ends of a third accommodating chamber 106 in whichthe automatic transmission portion 20 is accommodated coaxially with thesecond axis CL2.

The support wall 98 and support member 104 of the third casing portion12 c cooperate with the fourth casing portion 12 d to define a fourthaccommodating portion 108 in which the drive linkage 23 consisting ofthe mutually meshing drive and driven gears 19, 21 is accommodated. Thesupport wall 98 includes a cylindrical projection 99 extending in theaxial direction away from the second electric motor M2, that is, towardthe fourth casing portion 12 d, while the support member 104 includes acylindrical projection 105 extending in the same axial direction. Thedrive gear 19 is rotatably supported by the cylindrical projection 99via bearings 110, while the driven gear 21 is rotatably supported by thecylindrical projection 105 via bearings 112.

The input rotary member 14 and the power transmitting member 18 haveaxial end portions coupled together such that the axial end portion ofthe power transmitting member 18 is fitted in a hole formed in the axialend portion of the input rotary member 14, such that the input rotarymember 14 and the power transmitting member 18 are rotatable relative toeach other. The input rotary member 14 is rotatably supported at anintermediate axial portion thereof by the first casing portion 12 a, andat its above-indicated axial end portion by the above-indicated axialend portion of the power transmitting member 18, indirectly via needlebearings. The power transmitting member 18 is rotatably supportedindirectly by the support wall 96 via a needle bearing, and directly bythe support wall 98. In the present embodiment, the input rotary member14 and the power transmitting member 18 respectively function as thefirst and second input shafts. On the first input shaft 14, there arecoaxially disposed the first electric motor M1, hydraulically operatedfrictional coupling devices in the form of the switching clutch C0 andbrake B0, and power distributing mechanism 16. On the second input shaft18, there is coaxially disposed the second electric motor M2.

The stator M1 s of the first electric motor M1 is fitted in the secondcasing portion 12 b, in contact with the inner circumferential surfaceof the second casing portion 12 b, and the rotor M1 r is splined to atubular sun gear shaft 114 which has the first sun gear S1 formed at oneaxial end portion and which extends through the support wall 82.Accordingly, the rotor M1 r and the first sun gear S1 are rotatedtogether. The sun gear shaft 114 is rotatably supported by the outercircumferential surface of the input rotary member 14. The axial endportion of the input rotary member 14 which is remote from the engine 8is integrally fixed to the first carrier CA1, so that the first carrierCA1 is rotated together with the input rotary member 14. Accordingly,the input rotary member 14 also functions as an input shaft of the firstplanetary gear set 24 or the power distributing mechanism 16.

A support member 116 in the form of a circular disc is provided tosupport the cylindrical first ring gear R1 of the first planetary gearset 24, such that the support member 116 is splined to the innercircumferential surface of the first ring gear R1 and to the outercircumferential surface of an axial end portion of the powertransmitting member 18, so that the first ring gear R1 and the powertransmitting member 18 are rotated as a unit. The switching clutch C1 isdisposed between the support wall 82 and the first planetary gear set24, to selectively connect the first carrier CA1 and the sun gear shaft114, while the switching brake B0 is disposed radially outwardly of thefirst planetary gear set 24, more precisely, between the first planetarygear set 24 and the inner surface of the second casing portion 12 b, toselectively fix the sun gear shaft 114 to the second casing portion 12b.

The stator M2 s of the second electric motor M2 is fixed to the innersurface of the third casing portion 12 c by bolts 117, while the rotorM2 r of the second electric motor M2 is rotatably supported by thesupport wall 96 and the support wall 98 via a pair of bearings 102. Thetubular power transmitting member 18 has stepped axial portions havingdifferent diameters which decrease in the axial direction from thesupport wall 98 toward the engine 8. The power transmitting member 18extends through the rotor M2 r of the second electric motor M2, and issplined to the inner circumferential surface of the rotor M2 r, so thatthe power transmitting member 18 and the rotor M2 r are rotated as aunit. Accordingly, the power transmitting member 18 can be insertedthrough the second electric motor M2, first planetary gear set 24 andfirst electric motor M1, after the third casing 12 c in which the secondelectric motor M2 is fixed in place is assembled with respect to thesecond casing 12 b in which the first electric motor M1 and the firstplanetary gear set 24 are positioned in place. A cylindrical connectingmember 118 fixed to the inner circumferential surface of the drive gear19 is splined to the outer circumferential surface of the axial endportion of the power transmitting member which is remote from the engine8, so that the drive gear 19 is fitted on the above-described axial endportion of the power transmitting member 18 via the connecting member118, such that the drive gear 19 and the power transmitting member 18are rotated as a unit.

The first intermediate shaft 40, second intermediate shaft 42, outputrotary member 22 and differential drive gear 84 are arranged coaxiallywith the second axis CL2, in the axial direction in the order ofdescription from the driven gear 21 toward the side of the engine 8. Acylindrical connecting member 120 fixed to the inner circumferentialsurface of the driven gear 21 is splined to the axial end portion of thefirst intermediate shaft 40 which is remote from the second intermediateshaft 42. The third accommodating chamber 106 formed in the second andthird casing portions 12 b, 12 c and between the support member 104 andthe support wall 82 to accommodate the automatic transmission portion 20has stepped axial portions the inner circumferential surfaces of whichhave different diameters decreasing in the axial direction from thesupport wall 82 toward the driven gear 21. Accordingly, the automatictransmission portion 20 can be installed into the third accommodatingchamber 106 through an opening 121 of the chamber 106, in the absence ofthe support member 104. The support member 104 is fitted in a shoulderpart of the third casing portion 12 c, with high degrees of accuracy ofpositioning in the axial and radial directions, and is removably fixedto the third casing portion 12 c by bolts (not shown).

The third accommodating chamber 106 accommodating the automatictransmission portion 20 is not provided with any support wall, so thatthe axial dimension of the third accommodating chamber 106 is minimized.Described more specifically, the first intermediate shaft 40 isrotatably supported by the support member 104 via a needle bearing 122,and the axial end portion of the comparatively long second intermediateshaft 42 which is on the side of the first intermediate shaft 40 isfitted in a hole formed in the adjacent axial end portion of the firstintermediate shaft 40 and is rotatably supported by the firstintermediate shaft 40 via a bushing 122, while the axial end portion ofthe second intermediate shaft 4 which is on the side of the differentialdrive gear 84 is fitted in the tubular output rotary member 22 rotatablysupported by the support wall 82 via a needle bearing 126, and isrotatably supported by the output rotary member 22 via a bushing 128.Thus, the first intermediate shaft 40 and the output rotary member 22which respectively function as the input and output shafts of theautomatic transmission portion 20 are rotatably supported by the supportmember 104 and the support wall 82, while the second intermediate shaft42 which is disposed between the first intermediate shaft 40 and outputrotary member 22 and which functions as an intermediate shaft of theautomatic transmission portion 20 is rotatably supported at its oppositeaxial end portions by the first intermediate shaft 40 and the outputrotary member 22, without any intermediate support wall supporting thesecond intermediate shaft 42 which supports the second, third and fourthplanetary gear sets 26, 28, 30. Accordingly, the required axialdimension of the automatic transmission portion 20 can be reduced.

The sun gear shaft 114 is rotatably supported by the second intermediateshaft 42, and the first clutch C1 is disposed between the first andsecond intermediate shafts 40, 42, while the second clutch C2 isdisposed between the first intermediate shaft 40 and the sun gear shaft114. The second and third sun gears S2, S3 are formed integrally withthe sun gear shaft 114. The output rotary member 22 is connected to thefourth carrier CA4, and is splined to the shaft portion 84 b of thedifferential drive gear 84. The second and third brakes B2, B3 havefriction plates and pistons having an outside diameter smaller than theinside diameter of the opening 121 of the third accommodating chamber106, so that the second and third brakes B2, B3 can be installed in thethird accommodating chamber 106, through the opening 131 in the absenceof the support member 104. Similarly, a sub-assembly of the first andsecond clutches C1, C2 mounted on the outer circumferential surface ofthe first intermediate shaft 40, and a sub-assembly of the second, thirdand fourth planetary gear sets 26, 28, 30 mounted on the outercircumferential surface of the second intermediate shaft 42 have outsidediameters smaller than the inside diameter of the opening 121, so thatthose sub-assemblies can be installed in place in the thirdaccommodating chamber 106, through the opening 131 in the absence of thesupport member 104.

The vehicular drive system 10 constructed as described above isassembled as indicated in the flow chart of FIG. 14. In a first step K1,the first casing portion 12 a and the second casing portion 12 b areassembled together, and the first electric motor M1, differential drivegear 84 and final reduction gear device 36 are accommodated in the spacebetween the first casing portion 12 a and the second casing portion 12b, such that the first electric motor M1 is coaxial with the first axisCL1, while the differential drive ear 84 and final reduction gear device36 are coaxial with the respective second and third axes CL2, CL3. Thedifferential drive gear 84 is installed independently of and prior tothe installation of the automatic transmission portion 20.

In a second step K2, the input rotary member 14 is inserted to extendthrough the first electric motor M1 installed in the space between thefirst and second casing portions 12 a, 12 b, and the switching clutchC0, switching brake B9 and a sub-assembly of the first planetary geardevice 34 are installed in a portion of the space within the secondcasing portion 12 b, into which portion the axial end portion of theinput rotary member 14 remote from the engine 8 extends. It is notedthat the first and second steps K1 and K2 may be implemented afterfourth and fifth steps K4, K5 described below. In a third step K3, thesecond casing portion 12 (first separate casing), and the third casingportion (second separate casing) in which the second electric motor M2has been installed are assembled together, and the power transmittingmember 18 is inserted into the second electric motor M2 and the firstplanetary gear set 24.

In a fourth step K4, the piston and friction plates of the third brakeB3, and the piston and friction plates of the second brake B2 areinstalled in the third accommodating chamber 106, through the opening121 of the third casing portion 12 c, such that the third brake B3 islocated on one of opposite axial sides of the second brake B2 which isremote from the opening 121. Then, the sub-assembly of the second, thirdand fourth planetary gear sets 26, 28, 30 mounted on the secondintermediate shaft 42 is installed in the third accommodating chamber106. In this fourth step K4, the output rotary member 22 of theautomatic transmission portion 20 which is connected to the fourthcarrier CA4 of the fourth planetary gear set 30 is splined to the shaftportion 84 b of the differential drive gear 84 supported by the firstand second casing portions 12 a, 12 b already assembled together, sothat the output rotary member 22 and the differential drive gear 84 arerotated as a unit. In a fifth step K5, the support member 104 is fittedin the third casing portion 12 c, and fixed therein by bolts (notshown).

In a sixth step K6, the drive gear 19 and driven gear 21 arerespectively mounted on the support wall 98 and support member 104, viathe bearings 110, 112, respectively, such that the drive gear 19 isconnected by the connecting member 118 to the axial end portion of thepower transmitting member 18, while the driven gear 21 is connected bythe connecting member 120 to the axial end portion of the firstintermediate shaft 40, and the fourth casing 12 d is fixed to the thirdcasing portion 12 c, so as to cover the drive gear 19 and driven gear21.

In the present vehicular drive system 10, the support wall 82 of thesecond casing portion 12 b has oil passages through which a pressurizedworking oil is supplied from a shift control valve (not shown) to thehydraulically operated differential limiting device in the form of theswitching clutch C0 and switching brake B0, and to the frictionalcoupling devices in the form of the brakes B2, B3, etc. of the automatictransmission portion 20. Those oil passages include a clutch engagingoil passage 134 for supplying the working oil to an oil chamber 132 foradvancing a piston 130 of the switching clutch C0, as shown inenlargement in FIG. 15. The oil passages further include a brakeengaging oil passage 140 for supplying the working oil to an oil chamber138 for advancing first and second pistons 136 a, 136 b of the brake B3,as shown in enlargement in FIG. 16. In the oil chamber 138, the firstand second pistons 136 a, 136 b are movable in abutting contact witheach other. A stationary partition wall 142 is provided to divide aspace between the first and second pistons 136 a, 136 b, into two parts,so that a hydraulic pressure acts on the back surface of the firstpiston 136 a while an atmospheric pressure acts on the front surface ofthe second piston 136 b. Accordingly, the pistons 136 a, 136 b areadvanced by a large force based on a pressure-receiving surface which istwo times the cross sectional surface area of the oil chamber 138.

The support wall 98 of the third casing portion 12 c and the supportmember 104 fitted in the third casing portion 12 c have oil passages forsupplying a lubricant to the bearing portions and meshing portions ofthe various rotary members of the vehicular drive system 10. Forexample, the input rotary member 14 and the power transmitting member 18coaxial with the first axis CL1 have an axial oil passage 146 formed toextend in parallel with the first axis CL1, and a plurality of radialoil passages 148 formed to extend in the radial directions, as shown inFIGS. 11, 15 and 17, for introducing the lubricant to predeterminedlubricating points. The support wall 98 of the third casing portion 12 chas a lubricant passage 150 which receives a lubricant delivered from aregulator valve (not shown), and the power transmitting member 18 has alubricant inlet passage 152 formed in its radial direction incommunication with the lubricant passage 150, at an axial positionthereof opposed to the open end of the lubricant passage 150. Thelubricant passage 150 and the lubricant inlet passage 152 are locatedbetween the bearing 110 of the drive gear 19, and one of the twobearings 102 of the rotor M2 r of the second electric motor M2, which islocated on one side of the rotor M2 r remote from the engine 8.

The lubricant introduced through the lubricant passage 150 and lubricantinlet passage 152 is delivered through the axial passage 146 formedthrough the second input shaft in the form of the power transmittingmember 18, in the opposite axial directions, to the first planetary gearset 24 and to the drive gear 19, so that the bearings 86, the carrierCA1 of the first planetary gear set 24, the bearings 110, and the needlebearings are lubricated by the lubricant delivered through the radialoil passages 148 communicating with the axial passage 146. To thebearings 110 supporting the drive gear 19, the lubricant is suppliedthrough not only the radial passages 148, but also radial oil passages154 formed through the connecting member 118 so as to extend in theradial directions, and radial oil passages 156 formed through thecylindrical projection 99 so as to extend in the radial directions.

The first planetary gear set 24 constituting a part of the differentialmechanism is supported by the axial end portion of the powertransmitting member 18 and the axial end portion of the input rotarymember 14 which is fitted on the above-indicated axial end portion ofthe power transmitting member 18 such that the power transmitting member18 and the input rotary member 14 are rotatable relative to each other.These axial end portions of the power transmitting member 18 and inputrotary member 14 have respective radial passages 148 a, 148 b formed toextend in the radial direction, as shown in FIG. 15, so that thelubricant supplied from the axial oil passage 146 is delivered throughthe radial passages 148 a, 148 b to the first planetary gear set 24, inparticular, to a portion between the carrier CA1 and pinion P1 on whicha relatively large load acts.

The first intermediate shaft 40, second intermediate shaft 42, and shaftportion 84 b of the differential drive gear 84 have an axial oil passage160 formed to extend in parallel with the second axis CL2, and aplurality of radial oil passages 162 formed to extend in the radialdirections, as shown in FIGS. 12, 16 and 18, for introducing the workingfluid to predetermined lubricating points. The support member 104 has alubricant passage 164 through which the working oil delivered from aregulator valve (not shown) is supplied as the lubricant. The firstintermediate shaft 40 has a plurality of radial lubricant inlet passages166 in communication with the lubricant passage 164, at an axialposition thereof opposed to the open end of the lubricant passage 164.Accordingly, the pressurized working oil supplied to the axial passage160 through the lubricant passage 164 and lubricant inlet passages 166is delivered through the radial oil passages 162 to the bearings 112,second, third and fourth planetary gear sets 26, 28, 30 of the automatictransmission portion 20, frictional coupling devices C1, C2, B1, B2, B3of the automatic transmission portion 20, bearings 88 and the bushings.To the bearings 112 supporting the driven gear 21, the lubricant issupplied through the radial oil passages 162, radial oil passages 168formed through the connecting member 120 so as to extend in the radialdirections, and radial oil passages 170 formed through the cylindricalprojection 105 so as to extend in the radial directions.

As described above, the working oil is supplied from the lubricantpassage 164 of the support member 104 to the axial passage 160 formedthrough the first and second intermediate shafts 40, 41, through thelubricant inlet passages 166 formed at an axially intermediate positionof the first intermediate shaft 40. Accordingly, the working oil isdelivered in the opposite axial directions to the driven gear 21 and tothe automatic transmission portion 20, and the distances to the radialoil passages 162 provided at the lubricating points of the automatictransmission 20 are reduced, and the required cross sectional surfacearea of the axial passages 160 can be reduced.

The first casing portion 12 a also has a lubricant passage 172 forsupplying the working oil to the axial passage 160, so that the workingoil is supplied through the lubricant passage 172 to a portion of theaxial passage 160 within the shaft portion 84 b of the differentialdrive gear 84, for lubricating the pair of bearings 88. The lubricant isdelivered through the axial passage 160 to the teeth of the outer gearportion 84 a of the differential drive gear 84 and to one of the twobearings 88 on the side of the driven gear 21, through a gap between theshaft portion 84 b and the second intermediate shaft 42, and a gapbetween the output rotary member 22 and the shaft portion 84 b which aresplined to each other. The lubricant is also delivered through the axialpassage 160 to the other bearing 88 on the side of the engine 8 and theteeth of the outer gear portion 84 a, through a radial oil passage 174formed through the shaft portion 84 b at an axial position thereofcorresponding to that bearing 88, and a radial groove 176 formed in theend face of the outer gear portion 84 a. Thus, the axial passage 160 issupplied with a sufficient amount of lubricant through the lubricantpassage 172, radial passage 174 and radial groove 176, as well asthrough the lubricant passage 164 formed through the support member 104.

As shown in FIG. 16, the inner circumferential surface of the outer gearportion 84 a of the differential drive gear 84 has a splined axialportion Sda on the side remote from the automatic transmission portion20. This splined axial portion Sda is splined to a splined axial portionSdb of the outer circumferential surface of the shaft portion 84 b,which is on the side remote from the automatic transmission portion 20.The other axial portion of the inner circumferential surface of theouter gear portion 84 a which is on the side of the automatictransmission portion 20 is snugly fitted on the other axial portion ofthe outer circumferential surface of the shaft portion 84 b which is onthe side of the automatic transmission portion 20. Between the outergear portion 84 a and the pair of bearings 88, there are interposed apair of thrust bearings 178, at predetermined axial positions, forreceiving axial loads acting on the differential drive gear 84.

In the present vehicular drive system 10, the input-side hydraulicallyoperated frictional coupling devices in the form of the clutches C1 andC2 are supplied with the working fluid through oil passages formedthrough the support member 104 fitted in the third casing portion 12 c.Those oil passages include a clutch engaging oil passage 184 forsupplying the working oil to an oil chamber 192 for advancing a piston180 of the clutch C1, as shown in enlargement in FIG. 18.

In the vehicular drive system 10 constructed according to the presentembodiment of the invention, the input rotary member 14 (first inputshaft) is rotatably supported by the first casing portion 12 a (firstsupport portion) provided on the housing 12 and the axial end portion ofthe power transmitting member 18 (second input shaft), and the powertransmitting member 18 is rotatably supported by the support wall 96(third support portion) and the support wall 98 (fourth support portion)that are provided on the housing 12. Thus, only the first casing portion12 a, the axial end portion of the power transmitting member 18, and thesupport walls 96, 98 are used to rotatably support the input rotarymember 14 and the power transmitting member 18, with high degrees ofradial bearing accuracy and concentricity, and the axial end portion ofthe power transmitting member 18 is used to rotatably support the inputrotary member 14 at its axial end portion, so that the required axialdimension of the vehicular drive system 10 can be effectively reduced.

The present vehicular drive system 10 is further arranged such that thepower transmitting member 18 (second input shaft) is provided with thesupport member 116 in the form of the circular disc splined to an outercircumferential surface thereof, such that the support member 116supports a rotary element in the form of the ring gear R1 of the firstplanetary gear set 24 (differential mechanism), so that the differentialmechanism and the power transmitting member 18 can be easily assembled.

The present vehicular drive system 10 is further arranged such that thepower transmitting member 18 (second input shaft) supports the rotor M2r of the second electric motor M2, so as to be rotated with the rotor M2r, and such that the rotor M2 r is rotatably supported by the supportwall 96 (third support portion) and the support wall 98 (fourth supportportion). Thus, the rotor M2 r of the second electric motor M2 having acomparatively large load is rotatably supported by the two support walls96, 98.

The present vehicular drive system 10 is also arranged such that therotor M1 r of the first electric motor M1 is rotatably supported by thefirst casing 12 a (first support portion) and the support wall 82(second support portion), so that the input rotary member 14 (firstinput shaft) does not receive the load of the rotor M1 r of the firstelectric motor M1, whereby a structure for supporting the input rotarymember 14 can be simplified.

The present vehicular drive system 10 is further arranged such that thedrive gear 19 is fitted on the axial end portion of the powertransmitting member 18 (second input shaft) which is opposite to itsaxial end portion supporting the input rotary member 14 (first inputshaft) and at which the power transmitting member 18 is supported by thesupport wall 98 (fourth support portion), so that the drive gear 19having a comparatively large diameter and a comparatively large load isrotatably supported primarily by the support wall 98.

In the present vehicular drive system 10, the housing 12 includes thethree separate axial portions in the form of the cap-shaped first casingportion 12 a, cylindrical second casing portion 12 b and cylindricalthird casing portion 12 c. The above-described first support portion isformed integrally with said cap-shaped first casing portion 12 a, andthe above-described second support portion in the form of the supportwall 82 is formed integrally with an axially intermediate part of thecylindrical second casing portion 12 b. Further, the above-describedthird support portion in the form of the support wall 96 is fixed to anaxial end portion of the cylindrical third casing portion 12 c which ison the side of the engine 8 (vehicle drive power source), and theabove-described fourth support portion in the form of the support wall98 is formed integrally with an axial end portion of the cylindricalthird casing portion 12 c which is remote from the engine 8 (vehicledrive power source). In the present drive system 10, the input rotaryelement 14 is rotatably supported by the first support portion formed onthe first casing portion 12 a, and the axial end portion of the powertransmitting member 18, while the power transmitting member 18 isrotatably supported by the support wall 96 fixed to the axial endportion of the third casing portion 12 c on the side of the engine 8,and the support wall 98 formed at the other axial end portion of thethird casing portion 12 c remote from the engine 8. Thus, the inputrotary member 14 and the power transmitting member 18 are supported withhigh degrees of radial bearing accuracy and concentricity. Further, theabsence of any support wall to support the input rotary member 14 at itsaxial end remote from the engine 8, and the utilization of the axial endportion of the power transmitting member 18 to support the input rotarymember 14 make it possible to reduce the required axial dimension of thevehicular drive system 10.

In the present vehicular drive system 10, the second support portion inthe form of the support wall 82 is formed integrally with the secondhousing portion 12 b, by which the rotor M1 r of the first electricmotor M1 is rotatably supported and which has the clutch engaging oilpassage 134 for supplying the pressurized working fluid to engage theswitching clutch C0 that is a part of the differential limiting devicefor controlling the differential function of the power distributingmechanism 16.

Embodiment 2

There will be described other embodiments of the present invention. Inthe following description of the other embodiments, the same referencesigns as used in the first embodiment will be used to identify thefunctionally identical elements, redundant description of which isomitted.

Referring to the fragmentary cross sectional view of FIG. 19, there isshown a part of a vehicular drive system 186 according to the secondembodiment of this invention. This drive system 186 is different fromthe drive system 10 of the first embodiment, only in that a drivelinkage 188 is provided in place of the drive linkage 23. As shown inFIG. 19, the drive linkage 188 includes a drive sprocket 190, a drivensprocket 192, and a connecting belt 194 which is formed of a metal orresin and which connects the drive and driven sprockets 190, 192. Thedrive sprocket 190 is mounted on the axial end portion of the powertransmitting member 18 through the connecting member 118 such that thedrive sprocket 190 and the power transmitting member 18 are rotated as aunit about the first axis CL1. The second sprocket 192 is mounted on theaxial end portion of the first intermediate shaft 40 through theconnecting member 120 such that the driven sprocket 192 and the firstintermediate shaft 40 are rotated as a unit about the second axis CL2.Thus, the drive linkage 188 is arranged to transmit a drive force fromthe power transmitting member 18 to the first intermediate shaft 40 suchthat the first intermediate shaft 40 is rotated in the same direction asthe power transmitting member 18. The present second embodiment hassubstantially the same advantages as the preceding embodiments.

Embodiment 3

Referring next to the fragmentary cross sectional view of FIG. 20, thereis shown a part of a vehicular drive system 196 according to the thirdembodiment of the invention. This drive system 196 is different from thedrive system 10 of the first embodiment, in that the axial position ofthe engine 8 is opposite to that in the first embodiment, and in that anidler gear 200 is interposed between the differential drive gear 84 andthe large-diameter gear 31 of the final reduction gear device 36. Theidler gear 200 is rotatably supported by the first and second casingportions 12 a, 12 b, via bearings 198. In the present third embodiment,a fourth axis CL4 is provided between and in parallel to the second andthird axes CL2, CL3, and the idler gear 200 is supported rotatably aboutthe fourth axis CL4, in meshing engagement with the differential drivegear 84 and the large-diameter gear 31 of the final reduction geardevice 36. The idler gear 200 transmits a rotary motion from thedifferential drive gear 84 to the large-diameter gear 31, without aspeed change of the rotary motion. The present third embodiment hassubstantially the same advantages as the preceding embodiments.

Embodiment 4

Referring to the schematic view of FIG. 21, there is shown anarrangement of a vehicular drive system 210 according to the fourthembodiment of this invention, which includes an automatic transmissionportion 212, and which is accommodated within the housing 12, as in thepreceding embodiments. This drive system 210 is different from the drivesystem 10 of the first embodiment of FIG. 1, in that the drive linkage188 is provided in place of the drive linkage 23, as in the secondembodiment, while the idler gear 200 is interposed between thedifferential drive gear 84 and the large-diameter gear 31 of the finalreduction gear device 36, as in the third embodiment, and in that theautomatic transmission portion 212 of Ravigneaux type including twoplanetary gear sets 26, 28 is provided in place of the automatictransmission portion 20.

The automatic transmission portion 212 includes a single-pinion typesecond planetary gear set 26, and a single-pinion type third planetarygear set 28. The third planetary gear set 28 has: a third sun gear S3; aplurality of mutually meshing third planetary gears P3; a third carrierCA3 supporting the third planetary gears P3 such that each of the thirdplanetary gears P3 is rotatable about its axis and about the axis of thethird sun gear S3; and a third ring gear R3 meshing with the third sungear S3 through the third planetary gears P3. For example, the thirdplanetary gear set 28 has a gear ratio ρ3 of about 0.315. The secondplanetary gear set 26 has: a second sun gear S2; a second planetary gearP2 formed integrally with one of the third planetary gears P3; a secondcarrier CA2 formed integrally with the third carrier CA3; and a secondring gear R2 formed integrally with the third ring gear R3 and meshingwith the second sun gear S2 through the second planetary gear P2. Forexample, the second planetary gear set 26 has a gear ratio ρ2 of about0.368. The automatic transmission portion 212 is of the Ravigneaux typein which the second and third carriers CA2, CA3 are integral with eachother, while the second and third ring gears R2, R3 are integral witheach other. The diameter or number of teeth of the second planetary gearP2 which is integral with one of the third planetary gears P3 may bedifferent with that of the third planetary gear P3, The second planetarygear P2 may be formed separately from the third planetary gears P3.Similarly, the second carrier CA2 and the second ring gear R2 may beformed separately from the respective third carrier. CA3 and ring gearR3. Where the numbers of teeth of the second sun gear S2, second ringgear R2, third sun gear S3 and third ring gear R3 are represented byZS2, ZR2, ZS3 and ZR3, respectively, the above-indicated gear ratios ρ2and β3 are represented by ZS2/ZR2 and ZS3/ZR3, respectively.

In the automatic transmission portion 212, the second sun gear S2 isselectively connected to the first intermediate shaft 40 through thesecond clutch C2, and selectively fixed to the housing 12 through thefirst brake B1. The second carrier CA2 and the third carrier CA3 areselectively connected to the first intermediate shaft 40 through thethird clutch C3, and selectively fixed to the housing 12 through thesecond brake B2, while the second ring gear R2 and the third ring gearR3 are fixed to the output rotary member 22. The third sun gear S3 isselectively connected to the first intermediate shaft 40 through thefirst clutch C1. The present fourth embodiment has substantially thesame advantages as the preceding embodiments:

In the vehicular drive system 210 constructed as described above, one ofa first gear position (first speed position) through a fifth gearposition (fifth speed position), a reverse gear position (rear driveposition) and a neural position is selectively established by engagingactions of a corresponding combination of the frictional couplingdevices selected from the above-described switching clutch C0, firstclutch C1, second clutch C2, third clutch C3, switching brake B0, firstbrake B1 and second brake B2, as indicated in the table of FIG. 22. Inthe present embodiment, too, the power distributing mechanism 16 isprovided with the switching clutch C0 and brake B0, so that the powerdistributing mechanism 16 can be selectively placed by engagement of theswitching clutch C0 or switching brake B0, in the fixed-speed-ratioshifting state in which the power distributing mechanism 16 is operableas a transmission having a single gear position with one speed ratio ora plurality of gear positions with respective speed ratios, as well asin the continuously-variable shifting state in which the powerdistributing mechanism 16 is operable as a continuously variabletransmission, as described above. In the present vehicular drive system210, therefore, a step-variable transmission is constituted by theautomatic transmission portion 212, and the power distributing mechanism16 which is placed in the fixed-speed-ratio shifting state by engagementof the switching clutch C0 or switching brake B0, and a continuouslyvariable transmission is constituted by the automatic transmissionportion 212, and the power distributing mechanism 16 which is placed inthe continuously-variable shifting state, with none of the switchingclutch C0 and brake B0 being engaged.

Embodiment 5

Referring to the schematic view of FIG. 23, there is shown anarrangement of a vehicular drive system 216 according to the fifthembodiment of this invention, which includes an automatic transmissionportion 214, and which is accommodated within the housing 12, as in thepreceding embodiments. This drive system 216 is different from the drivesystem 10 of the first embodiment, in that the axial position of theengine 8 is opposite to that in the first embodiment, and the automatictransmission portion 214 is provided in place of the automatictransmission portion 20.

The automatic transmission portion 214 includes a single-pinion typesecond planetary gear set 26 having a gear ratio ρ2 of about 0.532, anda single-pinion type third planetary gear set 28 having a gear ratio ρ3of about 0.418. The second sun gear S2 of the second planetary gear set26 and the third sun gear S3 of the third planetary gear set 28 areformed integrally with each other, selectively connected to the firstintermediate shaft 40 through the second clutch C2, and selectivelyfixed to the housing 12 through the first brake B1. The second carrierCA2 of the second planetary gear set 26 and the third ring gear R3 ofthe third planetary gear set 28 are formed integrally with each other,and fixed to the output rotary member 22. The second ring gear R2 isselectively connected to the first intermediate shaft 40 through thefirst clutch C1, and the third carrier CA3 is selectively fixed to thehousing 12 through the second brake B2.

In the vehicular drive system 216 constructed as described above, one ofa first gear position (first speed position) through a fourth gearposition (fourth speed position), a reverse gear position (rear driveposition) and a neural position is selectively established by engagingactions of a corresponding combination of the frictional couplingdevices selected from the above-described switching clutch C0, firstclutch C1, second clutch C2, switching brake B0, first brake B1 andsecond brake B2, as indicated in the table of FIG. 24. Those gearpositions have respective speed ratios γ (input shaft speedN_(IN)/output shaft speed N_(OUT)) which change as geometric series. Inthe present embodiment, too, the power distributing mechanism 16 isprovided with the switching clutch C0 and brake B0, so that the powerdistributing mechanism 16 can be selectively placed by engagement of theswitching clutch C0 or switching brake B0, in the fixed-speed-ratioshifting state in which the power distributing mechanism 16 is operableas a transmission having a single gear position with one speed ratio ora plurality of gear positions with respective speed ratios, as well asin the continuously-variable shifting state in which the powerdistributing mechanism 16 is operable as a continuously variabletransmission, as described above.

Embodiment 6

Referring to the schematic view of FIG. 25, there is shown anarrangement of a vehicular drive system 220 according to the fifthembodiment of this invention, which includes an automatic transmissionportion 218, and which is accommodated within the housing 12, as in thepreceding embodiments. This drive system 220 is different from the drivesystem 210 of the fourth embodiment of FIG. 21, in that the automatictransmission portion 218 is provided in place of the automatictransmission portion 212, and the drive linkage 23 is provided in placeof the drive linkage 188, while the idler gear 200 is not provided.

The automatic transmission portion 218 includes a double-pinion typesecond planetary gear set 26, and a single-pinion type third planetarygear set 28. The second planetary gear set 26 has: a second sun gear S2;a plurality of mutually meshing second planetary gears P2; a secondcarrier CA2 supporting the second planetary gears P2 such that each ofthe second planetary gears P2 is rotatable about its axis and about theaxis of the second sun gear S2; and a second ring gear R2 meshing withthe second sun gear S2 through the second planetary gears P2. Forexample, the second planetary gear set 26 has a gear ratio ρ2 of about0.461. The third planetary gear set 28 has: a third sun gear S3; a thirdplanetary gear P3; a third carrier CA3 supporting the third planetarygear P3 such that the third planetary gear P3 is rotatable about itsaxis and about the axis of the third sun gear S3; and a third ring gearR3 meshing with the third sun gear S3 through the third planetary gearP3. For example, the third planetary gear set 28 has a gear ratio ρ3 ofabout 0.368.

The automatic transmission portion 218 is provide with the first andsecond brakes B1, B2 and the first, second and third clutches C1-C3. Thesecond sun gear S2 is selectively connected to the power transmittingmember 18 through the first clutch C1, and the second carrier CA2 andthe third sun gear S3 are formed integrally with each other, selectivelyconnected to the first intermediate shaft 40 through the second clutchC2, and selectively fixed to the housing 12 through the first brake B1.The second ring gear R2 and the third carrier CA3 are formed integrallywith each other, selectively connected to the first intermediate shaft40 through the third clutch C3, and fixed to the housing 12 through thesecond brake B2, while the third ring gear R3 is fixed to the outputrotary member 22. In the present sixth embodiment, the shifting actionsof the automatic transmission portion 218 are performed as indicated inthe table of FIG. 22 used in the fourth embodiment. The present sixthembodiment has substantially the same advantages as the precedingembodiments.

While the preferred embodiments of this invention have been describedabove by reference to the accompanying drawings, for illustrativepurpose only, it is to be understood that the present invention may beembodied with various changes and modifications, as described below.

In the vehicular drive systems 10, 210, 216, 220 of the illustratedembodiments, the power distributing mechanism 16 is placed selectivelyin one of its differential state and non-differential state, so that thedrive system 10 is switchable between the continuously-variable shiftingstate in which the drive system is operable as an electricallycontrolled continuously-variable transmission, and the step-variableshifting state in which the drive system is operable as a step-variabletransmission. However, the switching between the continuously-variableshifting state and the step-variable shifting state is one form of theswitching between the differential state and the non-differential stateof the power distributing mechanism 16. For instance, the powerdistributing mechanism 16 may be operated as a step-variabletransmission the speed ratio of which is variable in steps, even whilethe power distributing mechanism 16 is placed in the differential state.In other words, the differential state and the non-differential state ofthe drive system 10, 210, 216, 220 (power distributing mechanism 16) donot necessarily correspond to the continuously-variable shifting stateand the step-variable shifting state, respectively, and the drive system10 need not be switchable between the continuously-variable shiftingstate and the step-variable shifting state.

In the power distributing mechanism 16 in the illustrated embodiments,the first carrier CA1 is fixed to the engine 8, and the first sun gearS1 is fixed to the first electric motor M1 while the first ring gear R1is fixed to the power transmitting member 18. However, this arrangementis not essential. The engine 8, first electric motor M1 and powertransmitting member 18 may be fixed to any other elements selected fromthe three elements CA1, S1 and R1 of the first planetary gear set 24.

While the engine 8 is directly fixed to the differential mechanism inputshaft 14 in the illustrated embodiments, the engine 8 may be operativelyconnected to the input shaft 14 through any suitable member such asgears and a belt, and need not be disposed coaxially with the inputshaft 14.

Although the power distributing mechanism 16 in the illustratedembodiments is provided with the switching clutch C0 and the switchingbrake B0, the power distributing mechanism 16 need not be provided withboth of the switching clutch C0 and brake B0. While the switching clutchC0 is provided to selectively connect the first sun gear S1 and thefirst carrier CA1 to each other, the switching clutch C0 may be providedto selectively connect the first sun gear S1 and the first ring gear R1to each other, or selectively connect the first carrier CA1 and thefirst ring gear R1. Namely, the switching clutch C0 may be arranged toconnect any two elements of the three elements of the first planetarygear set 24.

While the switching clutch C0 is engaged to establish the neutralposition N in the drive systems 10, 210, 216, 220 of the illustratedembodiments, the switching clutch C0 need not be engaged to establishthe neutral position.

The frictional coupling devices used as the switching clutch C0,switching brake B0, etc. in the illustrated embodiments may be replacedby a coupling device of a magnetic-power type, an electromagnetic typeor a mechanical type, such as a powder clutch (magnetic powder clutch),an electromagnetic clutch and a meshing type dog clutch.

Each of the drive systems 10, 210, 216, 220 according to the illustratedembodiments is a drive system for a hybrid vehicle in which the drivewheels 38 can be driven by not only the engine 8 but also the firstelectric motor or the second electric motor M2. However, the principleof the present invention is applicable to a vehicular drive system inwhich the power distributing mechanism 16 is not operable in a hybridcontrol mode, and functions only as a continuously variable transmissionso-called an “electric CVT”.

While the power distributing mechanism 16 is constituted by oneplanetary gear set in the illustrated embodiments, the powerdistributing mechanism 16 may be constituted by two or more planetarygear sets. In this case, the power distributing mechanism 16 functionsas a transmission having three or more gear positions in thefixed-speed-ratio shifting state.

In the illustrated embodiments, the automatic transmission portion 20includes the three planetary gear sets 26, 28 and 30. However, theautomatic transmission portion 20 may be replaced by a speed reducingmechanism including one planetary gear set, as disclosed inJP-2003-301731A, and may include four or more planetary gear sets.Namely, the construction of the automatic transmission is not limited tothe details of the illustrated embodiments, in the number of theplanetary gear sets, the number of the gear positions, and the selectiveconnections of the clutches C and brakes B to the elements of theplanetary gear sets.

The vehicular drive systems 10, 210, 216, 220 may be modified such thatthe second electric motor M2 is disposed on one axial side of the drivegear 19 which is remote from the first planetary gear set 24, and/orsuch that the first clutch C1 is disposed on one axial side of thedriven gear 21 which is remote from the second planetary gear set 26.

Although the support walls 82, 98 in the illustrated embodiments areformed integrally with the housing 12, these support walls may be formedseparately from the housing 12 and fixed to the housing 12. Conversely,the support wall 96 formed separately from the housing 12 and fixed tothe housing 12 may be formed integrally with the housing 12.

The second electric motor M2 may be disposed at any position in thepower transmitting path between the power transmitting member 18 and thedrive wheels 38, and may be operatively connected to the powertransmitting path, either directly, or indirectly via a belt, gears, aspeed reducing device, etc.

It is to be understood that the embodiments described above are givenfor illustrating the present invention and that the invention may beembodied with various other changes and modifications which may occur tothose skilled in the art.

1-17. (canceled)
 18. A vehicular drive system accommodated in a housingand comprising: a first input shaft that receives a vehicle drive forcegenerated by a vehicle drive power source; and a differential mechanismoperable to distribute said vehicle drive force received from said firstinput shaft to a first electric motor and a second input shaft, saidfirst and second input shafts being disposed coaxially with a first axissuch that said second input shaft is disposed downstream of said firstinput shaft, wherein said first input shaft is rotatably supported by afirst support portion provided on said housing and an axial end portionof said second input shaft; said second input shaft is rotatablysupported by a third support portion and a fourth support portion thatare provided on said housing; and a drive gear fitted on an axial endportion of said second input shaft which is opposite to the axial endportion thereof supporting said first input shaft.
 19. The vehiculardrive system according to claim 18, wherein a driven gear meshing withsaid driving gear and an automatic transmission are arranged on anintermediate shaft arranged on a second axis that is parallel to thefirst axis.
 20. The vehicular drive system according to claim 19,wherein said automatic transmission includes a plurality of planetarygear devices arranged coaxially.
 21. The vehicular drive systemaccording to claim 18, wherein said first input shaft further includes,in addition to said first electric motor and said differentialmechanism, a differential limiting device for selectively switching saiddifferential mechanism to a differential state operable to perform adifferential operation and a locked state operable to inhibit saiddifferential operation.
 22. The vehicular drive system according toclaim 21, wherein said differential mechanism operates as anelectrically continuously-variable transmission when the differentialoperation thereof is not limited by said differential limiting device,and operates as a step-variable transmission having a plurality ofshifting steps when the differential operation thereof is limited bysaid differential limiting device.
 23. The vehicular drive systemaccording to claim 22, wherein said differential mechanism includes afirst rotary member connected to said vehicle power drive source, asecond rotary element connected to said first electric motor, and athird rotary member connected to a second electric motor, and saidvehicular drive system further comprising switching control means forcontrolling said differential limiting device based on a vehiclepredetermined condition to switch said differential mechanism to thecontinuously-variable shifting state and the step-variable shiftingstate.
 24. The vehicular drive system according to claim 23, whereinsaid differential limiting device switches said differential mechanismto the continuously-variable shifting state or the step-variableshifting state, and switches to one of shifting steps of thestep-variable shifting state, and said switching control means switchessaid differential mechanism from the continuously-variable shiftingstate to the step-variable shifting state, and selects one of pluralshifting steps in the step-variable shifting state by controlling thedifferential limiting device based on the vehicle predeterminedcondition.
 25. The vehicular drive system according to claim 21, whereinsaid second electric motor is disposed on said second input shaft, andsaid driving gear is arranged at a location opposite to said vehicledrive power source with respect to said second electric motor.
 26. Thevehicular drive system according to claim 19, wherein said intermediateshaft has a first intermediate shaft rotatably supported by said fourthsupporting wall, and a second intermediate shaft of which first andsecond ends are respectively supported by said first intermediate shaftand an output member which is rotatably supported by said housing. 27.The vehicular drive system according to claim 21, wherein both a secondcase portion and a third case portion of said housing form a secondaccommodating chamber and a third accommodating chamber, saiddifferential mechanism and said second electric motor are accommodatedin the second accommodating chamber, and said automatic transmission isaccommodated in the third accommodating chamber.
 28. The vehicular drivesystem according to claim 18, wherein said second input shaft includes asupport member in a form in of a circular disc splined to an outercircumferential surface such that the support member supports a rotaryelement of said differential mechanism.
 29. The vehicular drive systemaccording to claim 18, further comprising a second electric motorreceiving electric power from said first electric motor to generate anelectric drive force disposed in a power transmitting path between saidsecond input shaft and a drive wheel of a vehicle, and wherein saidsecond input shaft supports a rotor of said second electric motor, so asto be rotated with said rotor, and said rotor being rotatably supportedby said third and fourth support portions.
 30. The vehicular drivesystem according to claim 18, wherein said first electric motor includesa rotor rotatably supported by said first support portion and a secondsupport portion provided on said housing.
 31. The vehicular drive systemaccording to claim 18, wherein said housing includes three separateaxial portions in a form of a cap-shaped first casing portion, acylindrical second casing portion, and a cylindrical third casingportion, said first support portion being formed integrally with saidcap-shaped first casing portion, said third support portion being fixedto an axial end portion of said cylindrical third casing portion that ison the side of said vehicle drive power source, and said fourth supportportion being formed integrally with an axial end portion of saidcylindrical third casing portion that is remote from said vehicle drivepower source.
 32. The vehicular drive system according to claim 30,wherein said second support portion is formed integrally with saidcylindrical second housing portion.
 33. The vehicular drive systemaccording to claim 32, wherein said differential mechanism is disposedradially outwardly of said first input shaft.
 34. The vehicular drivesystem according to claim 33, wherein said differential limiting deviceis disposed radially outwardly of said first input shaft.
 35. Thevehicular drive system according claim 19, wherein said first inputshaft further includes, in addition to said first electric motor andsaid differential mechanism, a differential limiting device forselectively switching said differential mechanism to a differentialstate operable to perform a differential operation and a locked stateoperable to inhibit said differential operation.
 36. The vehicular drivesystem according claim 20, wherein said first input shaft furtherincludes, in addition to said first electric motor and said differentialmechanism, a differential limiting device for selectively switching saiddifferential mechanism to a differential state operable to perform adifferential operation and a locked state operable to inhibit saiddifferential operation.
 37. The vehicular drive system according toclaim 22, wherein said second electric motor is disposed on said secondinput shaft, and said driving gear is arranged at location more remotefrom said vehicle drive power source than said second electric motor.38. The vehicular drive system according to claim 22, wherein both asecond case portion and a third case portion of said housing form asecond accommodating chamber and a third accommodating chamber, saiddifferential mechanism and said second electric motor are accommodatedin the second accommodating chamber, and said automatic transmission isaccommodated in the third accommodating chamber.
 39. The vehicular drivesystem according to claim 28, further comprising a second electric motorreceiving electric power from said first electric motor to generate anelectric drive force disposed in a power transmitting path between saidsecond input shaft and a drive wheel of a vehicle, and wherein saidsecond input shaft supports a rotor of said second electric motor, so asto be rotated with said rotor, and said rotor being rotatably supportedby said third and fourth support portions.
 40. The vehicular drivesystem according to claim 28, wherein said first electric motor includesa rotor rotatably supported by said first support portion and a secondsupport portion provided on said housing.
 41. The vehicular drive systemaccording to claim 29, wherein said first electric motor includes arotor rotatably supported by said first support portion and a secondsupport portion provided on said housing.
 42. The vehicular drive systemaccording to claim 28, wherein said housing includes three separateaxial portions in a form of a cap-shaped first casing portion, acylindrical second casing portion, and a cylindrical third casingportion, said first support portion being formed integrally with saidcap-shaped first casing portion, said third support portion being fixedto an axial end portion of said cylindrical third casing portion that ison the side of said vehicle drive power source, and said fourth supportportion being formed integrally with an axial end portion of saidcylindrical third casing portion that is remote from said vehicle drivepower source.
 43. The vehicular drive system according to claim 29,wherein said housing includes three separate axial portions in a form ofa cap-shaped first casing portion, a cylindrical second casing portion,and a cylindrical third casing portion, said first support portion beingformed integrally with said cap-shaped first casing portion, said thirdsupport portion being fixed to an axial end portion of said cylindricalthird casing portion that is on the side of said vehicle drive powersource, and said fourth support portion being formed integrally with anaxial end portion of said cylindrical third casing portion that isremote from said vehicle drive power source.
 44. The vehicular drivesystem according to claim 30, wherein said housing includes threeseparate axial portions in a form of a cap-shaped first casing portion,a cylindrical second casing portion, and a cylindrical third casingportion, said first support portion being formed integrally with saidcap-shaped first casing portion, said third support portion being fixedto an axial end portion of said cylindrical third casing portion that ison the side of said vehicle drive power source, and said fourth supportportion being formed integrally with an axial end portion of saidcylindrical third casing portion that is remote from said vehicle drivepower source.